Alt text and image captions serve distinct purposes in search discovery and accessibility. Use alt text to describe the image content for screen readers and search crawlers, whereas captions provide additional context for all users. Do not repeat the same text in both fields, as this creates a redundant experience for assistive technology users and misses opportunities for added search context.
Defining the Roles of Image Metadata
Understanding the specific function of each attribute ensures that you provide the right information to both users and search engines.
Alt Text (Alternative Text)
Alt text is functional. Its primary purpose is to describe the image for users who cannot see it, such as those using screen readers. Search engines use this text to understand the subject matter of the image.
- →Best for: Describing the content, action, or intent of the image.
- →Avoid: Stuffing keywords or stating image of.
Captions
Captions are visible text placed near the image. They provide context, such as identifying a person, a location, or an emotional response, that enhances the page content.
- →Best for: Adding value that the visual cannot convey alone.
- →Strategy: Use captions to tell the story; use alt text to describe the visual.
Filenames
Filenames provide the final signal to search engines about the image contents before they even parse the page.
- →Best for: Descriptive, hyphen-separated identifiers.
- →Example: Use blue-denim-jacket.jpg instead of IMG_1234.jpg.
Decision Guide: Where to Place Your Content
| Content Type | Alt Text | Caption | Filename |
|---|---|---|---|
| Subject Description | Yes | No | Yes |
| Location/Date | No | Yes | No |
| Keyword Relevance | Secondary | Secondary | Primary |
| Decorative Content | Empty (alt="") | No | No |
Illustrative Worked Example
Imagine you are publishing a blog post about an architectural project.
- →Filename: modern-library-reading-room.jpg (Clear, descriptive).
- →Alt Text: Wide shot of a modern library reading room with sunlight streaming through floor-to-ceiling windows onto wooden tables. (Describes what is visible).
- →Caption: The library's design focuses on maximizing natural light to reduce energy consumption, completed in 2025. (Provides relevant context that isn't just visual).
Handling Decorative Images
If an image is purely decorative—such as a background pattern, a divider, or an icon that adds no informational value—you must signal this to screen readers. Use an empty alt attribute (alt="") in your HTML. This tells assistive technology to skip the image entirely. If you omit the alt attribute, some screen readers will announce the filename, which creates a frustrating, cluttered experience for the user.
Verification and Limitations
How you verify your implementation depends on your development environment:
- →Check Accessibility: Use a browser-based screen reader or an accessibility auditing tool to ensure decorative images are ignored and descriptive images provide meaningful feedback.
- →Check SEO: Use the Inspect tool in your browser to verify that the alt tag is present and unique for every informative image.
- →Limitations: Note that while descriptive text helps search engines categorize your content, it does not guarantee ranking. Search engines also analyze page surrounding content, site authority, and load speed.
For a practical next step, audit your most popular page for any images currently using generic filenames like image1.jpg and update them to reflect the specific content they display.