Alt Text for SEO: How to Write It (And How to Generate It for Every Image Automatically)

What is alt text, and why does it matter for SEO?

Alt text (short for "alternative text") is a description attached to an image via the alt attribute in HTML. It exists primarily for accessibility — screen readers read it aloud so visually impaired users know what an image shows — but it also does real SEO work:

• Google Images ranking — Google can't "see" an image the way a human does. Alt text is one of the strongest signals it uses to understand and rank images in Google Images search, which drives real traffic for product and blog content.
• Broken-image fallback — if an image fails to load, the alt text displays in its place, so the page still makes sense.
• Context for the surrounding page — descriptive, keyword-relevant alt text reinforces what a page is about, alongside your title tag and body content.

Missing alt text isn't just a missed opportunity — on many sites it's also an accessibility compliance issue (WCAG 2.1 requires it for informational images).

What a good alt text looks like

<img src="red-running-shoes.jpg" alt="Red and white Nike running shoes, side view" />

Compare that to what most sites actually ship:

<img src="IMG_4821.jpg" alt="" />
<img src="product-photo-2.png" alt="image" />

Generic alternatives tell a screen reader little and give search engines weak context. A blank alt attribute is correct for a purely decorative image, but informative images need a concise description of their purpose in the surrounding page.

How to write alt text correctly

• Be specific and descriptive — describe what's actually in the image, not a vague category. "Woman hiking a mountain trail at sunset" beats "hiking photo."
• Keep it under ~125 characters — some screen readers cut off longer alt text, and Google doesn't need more than a concise description.
• Include the target keyword only if it's genuinely accurate — don't stuff "best running shoes 2026" into every image alt on the page. That reads as spam to both Google and screen reader users.
• Skip alt text (or use alt="") for purely decorative images — a background texture or divider icon doesn't need a description; an empty alt attribute tells screen readers to skip it entirely, which is the correct behavior.
• Don't start with "Image of" or "Picture of" — screen readers already announce it's an image. It's redundant and wastes your character budget.

Alt text by image type

• Product photos → include the product name, key visual attributes (color, angle), and material if relevant: "Blue ceramic coffee mug, 12oz, front view"
• Blog/article images → describe what's happening in the image in the context of the article, not a generic caption
• Team/headshot photos → name and role: "Sarah Chen, Head of Product"
• Charts/infographics → summarize the data shown, since a screen reader user can't visually parse a chart: "Bar chart showing organic traffic growth from 2K to 18K monthly visitors over 12 months"
• Logos → the company/brand name is usually sufficient

The problem: writing this by hand doesn't scale

A 10-page site might have 30–50 images. A mid-size e-commerce store can easily have thousands of product photos. Writing accurate, non-generic alt text for every single one by hand is realistically never going to happen — which is exactly why so many sites ship with blank or filename-based alt attributes across the board.

This is one of the areas AI is genuinely well-suited for: an image-description model can look at each image and generate an accurate, specific description in seconds, at any scale.

Generate alt text for every image automatically

Peak Visibility generates suggested alt text for every image found during a scan, as part of the same pass that builds your sitemap, meta tags, and schema markup. The output is a single alt-text.json file mapping each image URL to a suggested description — review and paste in, or use it as a first draft to edit from.

Paste your URL and get alt text for your whole site in under 3 minutes. Free for up to 5 pages, no credit card required.