Imagine opening an online course and discovering that several important images are missing. The diagrams are gone, the charts are invisible, and the screenshots that explain how to complete assignments have disappeared. You can still read the surrounding text, but you are missing information that other learners can access. Now imagine discovering that those images are technically present, but the descriptions provided for them are so vague that they offer almost no useful information.
For learners who use screen readers, this experience can be surprisingly common. An image may be accompanied by alternative text that says something like "image," "chart," or "screenshot," leaving the learner to guess what the visual communicates. In other cases, the alternative text contains an unnecessarily detailed description of every visible object without explaining why the image matters. Neither approach provides meaningful access to the instructional content.
Alternative text, commonly called alt text, is one of the simplest accessibility features to implement, yet it is also one of the easiest to misunderstand. Writing effective alt text requires more than describing what appears in an image. It requires understanding the image's purpose, its relationship to the surrounding content, and what learners need to know to achieve the learning objectives. This article examines what makes alt text effective, why context matters, and how instructional designers can write descriptions that make visual information more accessible without overwhelming learners.
What Is Alt Text, and Why Does It Matter?
Alternative text is a text-based alternative to non-text content, most commonly images. When a screen reader encounters an image with appropriate alt text, it can announce the description to the learner. This allows someone who cannot see the image to access information that might otherwise be unavailable. Alt text may also appear when an image fails to load, although its primary accessibility purpose is to communicate the image's meaning or function.
The Web Content Accessibility Guidelines (WCAG) establish expectations for providing text alternatives to non-text content. Under Success Criterion 1.1.1, non-text content generally needs a text alternative that serves an equivalent purpose, with specific exceptions for different types of content (World Wide Web Consortium [W3C], 2023). This requirement is particularly important in online education, where images frequently communicate concepts, demonstrate procedures, or provide information necessary for completing assignments.
However, meeting a technical requirement does not automatically mean the resulting description is useful. An image can have alt text and still create an accessibility barrier if that text fails to communicate the information learners need. Effective instructional design goes beyond checking whether an alternative exists. It considers whether the alternative actually supports understanding.
Alt Text Should Communicate Meaning, Not Just Appearance
One of the most common mistakes in writing alt text is focusing exclusively on what an image looks like. While visual details sometimes matter, they are not always the most important information. A description should communicate the image's purpose within the learning experience rather than simply cataloging everything visible.
Consider a photograph showing several students gathered around a table with laptops and notebooks. If the image appears on a course homepage to create a welcoming atmosphere, a brief description such as "Students collaborating around a table with laptops and notebooks" may be sufficient. The learner receives the relevant information without listening to unnecessary details about clothing, furniture, or background decorations.
Now imagine the same photograph appearing in a lesson about collaborative learning strategies. The image may be intended to demonstrate how students share resources, discuss ideas, and work together on a problem. In that context, a description emphasizing the collaborative activity may communicate the instructional purpose more effectively. The photograph has not changed, but the information learners need from it has.
This is why alt text cannot always be written effectively without understanding the surrounding content. Instructional designers must consider what the image contributes to the lesson and what information would be missing if the learner could not see it. The best description is not necessarily the most detailed one. It is the one that communicates the information that matters.
Context Changes Everything
An image does not have one universally correct alt text description. Its purpose can change depending on where and how it is used. The same image might require different descriptions in a history course, a graphic design course, or a professional development workshop because learners are expected to notice different information.
Imagine a photograph of a historical building. In an architectural history course, the relevant information might involve the building's structural features, materials, and design characteristics. In a political science course, the same photograph might illustrate the location where an important political event occurred. A description that works well for one learning objective may provide little useful information for the other.
Context also helps determine how much detail is necessary. If the surrounding paragraph already identifies the building and explains its historical importance, repeating that information in the alt text may be unnecessary. Instead, the description might focus on visual details that contribute something new. The goal is to provide an equivalent learning experience, not to repeat information simply because it appears near an image.
For instructional designers, this means alt text should be considered during course development rather than added mechanically at the end. Understanding why an image was selected makes it much easier to determine what its description should communicate. Accessibility becomes part of the instructional decision-making process rather than an administrative task completed after the course is built.
Not Every Image Needs a Description
One of the more surprising aspects of accessible design is that some images should not have descriptive alt text at all. Decorative images that do not communicate meaningful information may be marked so assistive technologies can skip them. This prevents learners from hearing unnecessary descriptions that interrupt the flow of the content.
For example, a decorative flourish separating two sections of a webpage may contribute to the visual appearance without communicating information. A background illustration might make a course homepage more attractive without affecting the learner's understanding of the content. Providing lengthy descriptions of these elements can create additional noise for screen reader users without offering an instructional benefit.
In HTML, a decorative image can often be identified using an empty alt attribute, written as alt="". This signals that the image does not require a spoken description. It is important to distinguish this from simply omitting the alt attribute, which may cause assistive technology to announce the image's filename or other unhelpful information.
The decision to mark an image as decorative should depend on its function, not merely its appearance. A photograph that seems decorative at first glance may communicate important information within a particular lesson. Likewise, an illustration that looks elaborate may contribute nothing essential to the instructional content. Determining the difference requires understanding the learning experience.
Writing Concise Alt Text Without Losing Meaning
Instructional designers sometimes struggle to balance brevity with sufficient detail. Descriptions that are too short may omit essential information, while descriptions that are too long can overwhelm learners or interrupt the surrounding content. The goal is to communicate the necessary information as efficiently as possible.
Consider a screenshot showing where students should select a button to submit an assignment. An overly vague description such as "Screenshot of an assignment page" does not help the learner understand what to do. A more useful description might say, "Assignment submission page with the Upload button located below the instructions." This provides actionable information that supports the learner's immediate task.
The appropriate length depends on the image's purpose. A simple photograph may require only a short phrase, while a complex instructional diagram may need a longer explanation. There is no universal word limit that makes alt text automatically accessible. What matters is whether the description communicates the image's relevant information clearly and without unnecessary repetition.
It is also generally unnecessary to begin every description with phrases such as "Image of" or "Picture of." Screen readers typically identify images as images, so repeating that information often adds little value. There are exceptions when the type of visual itself matters, such as distinguishing a photograph from an illustration or identifying a chart. The description should include those details when they contribute to understanding.
Charts and Graphs Require More Than a Label
Charts and graphs present particular challenges because they often communicate relationships, patterns, and comparisons that are difficult to summarize in a short sentence. Simply identifying a visual as a bar chart or line graph does not provide access to the information it contains. Learners need to understand what the data communicates and why it matters.
Imagine a line graph showing student participation declining throughout a semester. A description such as "Line graph of student participation" identifies the visual but does not communicate the pattern. A more useful short description might explain that participation steadily decreases over the semester, with the largest decline occurring after the midpoint. This gives learners access to the primary finding rather than merely the chart's format.
However, some charts contain more information than can reasonably fit into a short alt text description. In those cases, instructional designers should provide a brief alternative identifying the chart's purpose and a longer description or accessible data table elsewhere in the content. This allows learners to examine the information at a level of detail appropriate to the instructional task.
The goal is not forcing an entire data visualization into one alt text field. It is ensuring that learners can access the information necessary to interpret the chart, answer questions, and complete the learning activity. Sometimes that requires multiple accessible formats working together.
Complex Diagrams Need Thoughtful Alternatives
Instructional diagrams often communicate relationships that are difficult to express through a short description. Flowcharts, organizational charts, scientific illustrations, process diagrams, and concept maps may contain multiple elements connected through arrows, lines, or other visual indicators. A simple description identifying the diagram's subject may not provide enough information for learners to understand how those elements relate.
Consider a diagram illustrating the instructional design process. The visual might show learner analysis leading to learning objectives, which then inform assessment design and instructional activities. Arrows may also indicate that evaluation and revision occur throughout the process. A description that simply says "Diagram of the instructional design process" leaves out the relationships that make the visual useful.
A better approach may involve a short alt text description accompanied by a structured explanation in the surrounding content. The explanation can describe the sequence, relationships, and feedback loops in a way that learners can understand without seeing the diagram. If the diagram contains information essential to an assessment, the accessible alternative should provide sufficient detail for learners to complete that assessment.
Instructional designers should also consider whether the diagram itself is the best way to communicate the concept. Sometimes a clearly structured text explanation or accessible table can communicate the same relationships more effectively. Providing multiple representations can benefit learners who process information differently, not just those using assistive technology.
Screenshots Should Support the Task
Screenshots are common in online courses, particularly when instructors demonstrate how to use learning management systems, software applications, or online resources. Unfortunately, screenshots are also frequently accompanied by vague descriptions that provide little instructional assistance. A screenshot showing an entire webpage may contain dozens of visual elements, but only one or two may matter to the learner.
Effective alt text should focus on the action or information the screenshot is intended to communicate. If the purpose is to show students where to locate assignment feedback, the description should identify the relevant interface element rather than describing every menu, icon, and navigation option. The surrounding instructions should also explain the process clearly enough that learners are not dependent on the screenshot alone.
This becomes particularly important when interfaces change. A screenshot may show a button in a location that no longer matches the current software version. If instructions rely entirely on visual placement, learners may struggle when the interface is updated. Describing controls by their accessible names and functions, when possible, creates instructions that are more useful across different devices and interface layouts.
Screenshots should support instruction rather than carry all of it. When the written directions are clear and the image provides additional visual guidance, learners have more than one way to understand the task. That is a stronger approach than expecting everyone to interpret the same screenshot.
AI Can Help Draft Alt Text, but Human Review Still Matters
Artificial intelligence has made generating image descriptions faster and more convenient. Many platforms now offer tools that automatically suggest alt text based on image recognition. These features can provide a useful starting point, particularly when working with large collections of images. However, AI-generated descriptions should not automatically be treated as complete or instructionally appropriate.
An AI tool may accurately identify a photograph as showing a person standing beside a whiteboard. What it may not understand is that the whiteboard contains a diagram illustrating a particular learning concept. Similarly, AI might describe the colors and shapes within a chart without identifying the trend that learners are supposed to analyze. The description may be visually accurate while still missing the instructional purpose.
This is where instructional designers contribute something that automated tools cannot reliably supply: context. We understand why an image appears in the course, what learners are expected to notice, and how the visual supports the learning objectives. AI can help generate initial descriptions, but those descriptions still require review for accuracy, clarity, relevance, and accessibility.
Using AI responsibly means treating its suggestions as drafts rather than final answers. The technology can reduce repetitive work, but it should not replace the human judgment needed to determine whether the description actually supports learning. Accessibility is too important to leave entirely to automated interpretation.
Alt Text Is Only One Part of Accessible Images
Although alt text is essential, it cannot solve every accessibility issue associated with images. A chart with excellent alt text may still be difficult to interpret visually if it relies entirely on color to distinguish information. A screenshot may have a useful description but still be unreadable when enlarged because the original image has insufficient resolution. Accessibility requires considering how the visual functions for different learners.
Instructional designers should also evaluate color contrast, text embedded within images, image quality, and the availability of alternative formats. When important information appears as text inside an image, it is often better to provide that text as actual webpage content whenever possible. This makes the information easier to enlarge, select, translate, and access through assistive technologies.
The broader goal is ensuring that learners can obtain the information they need regardless of how they access the course. Alt text contributes to that goal, but it works best as part of an intentional approach to accessible course design. A technically compliant image is not necessarily an instructionally effective one.
Review Alt Text From the Learner's Perspective
One of the best ways to evaluate alt text is to consider whether the description would make sense without the image. If a learner heard only the alternative text and the surrounding content, would they understand the information the image contributes? Would they be able to complete the associated activity or answer questions about the visual? If not, the description may need revision.
Instructional designers can also review whether descriptions repeat information unnecessarily. If the surrounding paragraph already explains the image's meaning, the alt text may only need to communicate additional visual information. Conversely, if the image contains information that does not appear anywhere else, the alternative must provide access to that content. The relationship between the image and the surrounding instruction determines what is necessary.
This review process is particularly useful during course quality checks and accessibility remediation. Instead of treating alt text as a field that simply needs to contain something, reviewers should evaluate whether the description serves its intended purpose. That approach produces more meaningful accessibility improvements than checking only whether the field is populated.
Final Thoughts
Writing effective alt text is not about describing every visible detail or satisfying a technical requirement with the shortest possible phrase. It is about communicating the meaning and purpose of visual information so learners can access the same instructional content in different ways. Good alt text reflects the image's context, the learner's needs, and the learning objectives the visual supports.
For instructional designers, this requires thoughtful decisions about what information matters, how much detail is necessary, and when additional alternatives should be provided. Simple photographs may need brief descriptions, while complex charts and diagrams may require structured explanations or accessible data tables. Decorative images may need no spoken description at all. The important consideration is whether the learner receives the information necessary to participate meaningfully in the learning experience.
Accessibility often improves through decisions that seem small when considered individually. A clearer link label, a properly structured heading, or a thoughtfully written image description may take only a few moments to create. Yet those decisions can determine whether a learner accesses important information independently or encounters another unnecessary barrier.
The best alt text does not simply describe what an image looks like. It communicates what the learner needs to know.
References
CAST. (2024). CAST Universal Design for Learning guidelines version 3.0. https://udlguidelines.cast.org/
Web Accessibility Initiative. (n.d.). Images tutorial. World Wide Web Consortium. https://www.w3.org/WAI/tutorials/images/
Web Accessibility Initiative. (n.d.). An alt decision tree. World Wide Web Consortium. https://www.w3.org/WAI/tutorials/images/decision-tree/
World Wide Web Consortium. (2023). Web Content Accessibility Guidelines (WCAG) 2.2. https://www.w3.org/TR/WCAG22/