Alt text: describing purpose, not just appearance

Writing meaningful descriptions that help users understand why an image is there, not just what it looks like.

The fundamental shift

Most people approach alt text by describing what they see: "woman in blue shirt," "modern building with glass windows," "chart with colored bars." This approach misses the point entirely. Alt text isn't a visual description for people who can't see - it's a functional replacement that explains what role the image plays in your content.

The key question isn't "what does this look like?" but "why is this image here?" When you shift from describing appearance to explaining purpose, your alt text becomes genuinely useful for screen reader users, people with slow internet connections, and anyone whose images fail to load.

This purpose-first approach also benefits search engines, which use alt text to understand how images relate to surrounding content. But the primary beneficiary should always be users who need the alt text to understand your content completely.

Function over appearance

Consider a staff photo of Dr. Sarah Johnson in a white coat, smiling professionally. Appearance-focused alt text might say "woman with brown hair wearing white coat and smiling." Purpose-focused alt text would say "Dr. Sarah Johnson, Speech Pathologist."

The image's job is helping users connect a name with a person and establish professional credibility. Hair color and smile details don't serve that function - the identity and role do. Someone using a screen reader needs to know who this person is and why their photo appears on this page, not what they look like.

This same principle applies across different image types. A flowchart showing your referral process doesn't need description of "blue boxes and arrows" - it needs explanation of the actual process: "Referral process: GP referral leads to intake assessment, then scheduling, then first appointment."

The visual elements are just the delivery method. The information those elements convey is what matters for alt text.

When details matter

Sometimes visual details are the content, and detailed description becomes necessary. Medical images, therapy demonstration photos, or before-and-after progress images often require specific visual information because the appearance is the point.

For a photo showing proper hand positioning during therapy, you'd need detailed description: "Hand positioned with thumb and index finger forming circle, remaining fingers extended, demonstrating fine motor exercise technique." Here, the visual details are the instructional content that users need to understand or replicate.

Progress photos comparing before and after treatment results similarly need appearance details: "Before treatment: visible scarring across left cheek. After treatment: significantly reduced scarring with smooth skin texture." The visual change is the information the image provides.

The key is distinguishing between images where appearance conveys essential information and images where appearance is just the vehicle for delivering other information like identity, location, or process steps.

Practical approaches for common scenarios

Staff and professional photos work best with simple identification: "Dr. Johnson, Clinical Director" rather than physical descriptions. The photo's function is establishing identity and credibility, not conveying appearance details.
Location photos should focus on identification and navigation help: "Research facility entrance on James Street" tells users what they need to know for finding the location.
Charts and graphs need the data, not the visual design: "Monthly referrals increased from 45 in January to 78 in June" conveys the information better than "bar chart with six ascending bars." Consider whether complex data visualisations might work better as accessible tables with the chart as supplementary visual information.
Logos and branding simply need the organisation name: "The Kids Research Institute Australia" rather than descriptions of design elements.

Context changes everything

The same image might need different alt text depending on where it appears and what surrounding content discusses. A photo of a child using a communication device could be "Child using tablet communication app" in a services overview, "TouchChat app displaying symbol grid interface" in a product review, or "Emma, age 7, selecting 'I want' using her communication device" in a case study.

The surrounding text determines what information the alt text should provide. If the caption already identifies the person and context, your alt text can focus on visual details that add information rather than repeating what's already stated nearby.

This contextual approach prevents redundancy while ensuring that someone using alt text gets complete information. Read your content with only the alt text (covering the actual images) to test whether the flow makes sense and whether crucial information is missing.

Avoiding common problems

Don't start alt text with "image of" or "picture of" - screen readers already announce that it's an image. Don't use alt text for keyword stuffing or search optimisation at the expense of user clarity. Don't provide excessive detail about irrelevant visual elements when simpler identification serves the purpose better.

Keep alt text concise when possible - around 100-125 characters works well for most screen readers. For complex images requiring longer explanation, use brief alt text for essential information and provide detailed description in surrounding text or captions.

Test your alt text by reading your content while imagining you can't see the images. Does the alt text provide the information needed to understand the content fully? Would someone miss important information if they only had the alt text instead of the image?

Implementation workflow

Before writing alt text, look away from the image and read the surrounding content. Ask what someone would miss if the image disappeared, then write alt text that fills that gap. Focus on the image's function in your content rather than its visual characteristics.

Remember that good alt text serves real users trying to accomplish real goals with your content. When you focus on purpose rather than appearance, your alt text becomes a genuine tool for accessibility rather than a compliance checkbox.

Check your understanding

Copy and paste this to ChatGPT when you're ready for feedback:

I've been completing some questions as part of an SEO course. I'm currently answering questions for a section titled "Alt text: describing purpose, not just appearance". Please check my answers and let me know if I've understood the key ideas correctly. My responses are below.

1. A colleague argues that detailed visual descriptions make alt text "more comprehensive and helpful" and insists on describing clothing, facial expressions, and background details for all staff photos. Using examples from the lesson, analyse why this approach can actually reduce the effectiveness of alt text and create barriers for screen reader users.

2. What is the main difference between purpose-focused and appearance-focused alt text?

Purpose-focused describes visual details while appearance-focused explains function
Purpose-focused explains why an image is there while appearance-focused describes what it looks like
Purpose-focused is shorter while appearance-focused is more detailed
Purpose-focused includes keywords while appearance-focused doesn't

3. When would it be appropriate to include detailed visual descriptions in alt text?

When the image is particularly attractive or well-designed
When the visual details are necessary to understand the content or instruction
When the image file size is large and needs explanation
When you want to improve search engine optimisation

4. You have a photo of your clinic's waiting room that appears on your "About Us" page. The surrounding text talks about creating a welcoming environment for families. Write appropriate alt text for this image.

5. Which approach to logo alt text is most appropriate?

Describe the visual elements: "Blue text with speech bubble icon and modern typography"
Use the organisation name: "The Kids Research Institute Australia"
Explain the symbolism: "Logo representing communication and professional healthcare"
Include keywords: "Children's health research institute Perth paediatric studies logo"

6. Consider this scenario: Your website features a complex infographic showing the stages of child development from birth to age 5, with detailed timelines and milestone markers. The graphic appears on a page about early intervention services. A content editor suggests using brief alt text like "child development infographic" because "the details are too complex for alt text." Evaluate this approach and propose a strategy that balances accessibility requirements with practical limitations.

7. A stakeholder argues that spending time crafting purpose-focused alt text is "unnecessary perfectionism" because "search engines can now recognise images automatically." Analyse why this reasoning fundamentally misunderstands both the purpose of alt text and the current limitations of automated image recognition technology.