Image SEO: Alt Text, Names, Structured Data

Most sites treat images as decoration. Search engines treat them as content — content they cannot see directly, which means they lean heavily on the text signals you attach to each image. That gap between how you think about images and how Google reads them is where image SEO lives, and it is one of the few areas of SEO where an afternoon of careful work produces measurable, durable results.

The payoff is threefold. First, Google Images is a real traffic source — for recipes, products, tutorials, and anything visual, it can drive a meaningful slice of organic visits. Second, well-labeled images make your pages easier for search engines to understand, which helps the page rank, not just the image. Third, everything that helps image SEO also helps accessibility, and that is a rare case of two goals aligning perfectly rather than fighting.

This post covers the three text signals that matter most — alt text, file names, and structured data — with concrete rules for each, worked examples, and the WordPress-specific gotchas that trip people up.

How search engines actually read images

Google does run computer vision over images, and it has gotten good at recognizing objects, scenes, and even text inside pictures. But vision models produce generic labels — “dog on grass,” “person at desk” — not the specific context your page is about. For ranking decisions, Google still weighs the text around and attached to an image heavily. In rough order of influence:

Alt text — the single most direct description of the image.
Surrounding text — the paragraph before and after, the nearest heading, and captions. Captions get read more than body text by humans, and search engines appear to treat them as strong context too.
File name and URL path — a weaker signal, but a free one.
Structured data — the machine-readable layer that unlocks rich results like product thumbnails and recipe cards.
Page title and overall page topic — an image on a page about sourdough is assumed to relate to sourdough.

The practical implication: no single signal carries the day. An image named IMG_4382.jpg with empty alt text on a well-written page still gets some context. But an image with all signals aligned — descriptive name, precise alt text, a caption, and structured data — is the one that shows up in image results and rich snippets. You are stacking modest signals, and the stack is what wins.

Alt text: the rules that actually matter

Alt text has two jobs, and they are the same job: describe the image to someone (or something) that cannot see it. Screen readers read it aloud; search engines index it. Write for the screen reader user and the search engine benefit comes along for free.

The decision tree

Before writing anything, decide what kind of image you are dealing with:

Informative image (a product photo, a chart, a screenshot of steps): describe what it shows and why it is there. This is the case where alt text earns its keep.
Functional image (an image that is also a link or button): describe the destination or action, not the picture. A logo linking home should say “Acme Bakery home,” not “blue circle with wheat icon.”
Decorative image (dividers, ambient stock photos, background texture): use an empty alt attribute. Empty, not missing — an empty alt tells screen readers to skip the image; a missing one makes some of them read the file name aloud, which is miserable.
Image of text (avoid these, but if you must): the alt text is the text in the image, verbatim.

Writing rules for informative images

Be specific before being brief. “Dog” is useless. “Border collie catching a frisbee mid-jump at a park” is indexable and paints the picture. As a rule of thumb, aim for 8–15 words; stay under roughly 125 characters, since some older screen readers truncate around there.
Include your keyword when it is honest, skip it when it is not. If the page targets “standing desk setup” and the image shows a standing desk setup, say so. If it shows your office dog, do not wedge the keyword in. Keyword-stuffed alt text is one of the older spam signals in the book, and it reads terribly aloud.
Skip “image of” and “picture of.” Screen readers already announce it is an image. Start with the subject.
Context decides the description. The same photo of a laptop needs different alt text on a product page (“Framework 13 laptop with the bezel removed, showing modular ports”) than in a blog post about remote work (“laptop on a kitchen table next to a coffee mug”). Describe what the image means on this page.
For charts and infographics, state the takeaway. “Line chart showing organic traffic doubling between January and June” beats “traffic chart.” If the data matters, it should also live in the body text — alt text is a summary, not the only copy of the information.

Worked examples

Say you run a bakery site and the page is about ordering custom cakes.

Bad: cake — technically present, tells nobody anything.
Bad in the other direction: custom cakes birthday cakes wedding cakes cake shop near me best cakes — this is a spam signal, and a screen reader user hears a ransom note.
Good: Three-tier wedding cake with white buttercream and fresh eucalyptus, made for a June wedding — specific, natural, contains real search terms because the image really contains those things.

File names: small signal, zero excuses

A file name is a weak ranking signal on its own, but it costs nothing to get right and it compounds: it shows up in the image URL, in image sitemaps, and in the fallback context when other signals are missing. The rules fit on an index card:

Rename before you upload. This is the single most important habit. WordPress builds the file URL from the name at upload time, so DSC01234.jpg becomes a permanent URL. Renaming inside the media library later does not change the URL of the already-uploaded file.
Use lowercase kebab-case: three-tier-wedding-cake-buttercream.jpg. Hyphens, not underscores — search engines treat hyphens as word separators and underscores as glue.
Describe the image, not the page. Five or six words is plenty. You do not need the full keyword phrase of the page in every image name; that pattern across twelve images looks manufactured.
Never change file names on published pages without redirecting the old URL. An image URL that 404s loses whatever image-search equity it had, and Google can take months to re-index a replacement.

One rule of thumb for batch work: if you are uploading more than about ten images, rename them all locally first with a consistent pattern (subject-detail-variant.jpg). Two minutes of renaming beats trying to retrofit context later.

Structured data: where images earn rich results

Alt text and file names help images get understood. Structured data helps them get featured. Most rich results in Google — product cards, recipe carousels, article thumbnails — require or strongly prefer an image declared in schema markup, and the requirements are more specific than people expect.

The image rules inside schema types

Article / BlogPosting: Google asks for images in multiple aspect ratios (16x9, 4x3, 1x1) and recommends at least 1200px wide for large thumbnails. In practice this means your featured image should start at 1200x675 or larger; most WordPress SEO plugins generate the schema, but they can only reference the image you actually uploaded.
Product: the image property is effectively mandatory for product rich results. Multiple angles help; Google may show any of them.
Recipe: image is required, full stop. A recipe without a schema image will not appear in the recipe carousel no matter how good the ranking.
ImageObject with license metadata: if you create original photography, adding license and acquireLicensePage properties earns the “Licensable” badge in Google Images — worth doing if image licensing is part of your business, safely skippable otherwise.

Practical WordPress guidance

You almost never write this JSON-LD by hand. The realistic setup is:

Use an SEO plugin (or your theme’s built-in schema) to emit Article/Product/Recipe markup automatically from the featured image and post fields.
Verify with Google’s Rich Results Test on one representative page per template — not every page, just one per type. If the template passes, the type passes.
Check that the featured image meets the size floor (1200px wide is the safe rule of thumb) before publishing, because schema pointing at a 400px image quietly disqualifies you from large-thumbnail treatments.

Image sitemaps

An image sitemap (or image entries inside your regular sitemap) tells Google about images it might not discover by crawling — ones loaded by JavaScript, galleries, or CDN-hosted files on a different domain. Most WordPress SEO plugins include images in the sitemap automatically. The one check worth doing: if your images are served from a CDN subdomain or an external host, confirm they appear in the sitemap anyway. That is the scenario where the sitemap genuinely changes discovery, rather than just confirming what the crawler already found.

The WordPress-specific gotchas

Media library alt text vs. block alt text. The alt text field in the media library is a default. When you insert an image into a post, the block copies it — and from then on they are independent. Fixing the media library entry does not fix posts that already embedded the image. When auditing, check the rendered page, not the library.
Featured images often render without your alt text. Some themes output the featured image with empty or auto-generated alt. View source on a post and check what your theme actually prints.
The title attribute is not alt text. WordPress auto-fills the image title from the file name. The title attribute does close to nothing for SEO and most screen readers ignore it. Do not spend time on it; spend that time on alt text.
Captions are user-facing gold. They get read, they add crawlable context, and they are a natural place for specifics that would bloat alt text. Use them where a caption would genuinely help a human.

What not to bother with

Image SEO attracts busywork. Things you can skip with a clear conscience:

EXIF and IPTC metadata for rankings. Google has said it may use EXIF as a signal, but nobody has ever demonstrated a ranking effect worth the effort. Strip it (smaller files) or keep it (photographer credit); either is fine.
Alt text on every last decorative flourish. Empty alt is the correct treatment, not a wasted opportunity.
Geotagging images for local SEO. A persistent myth. Your Google Business Profile and on-page location text do this job; coordinates baked into a JPEG do not.
Rewriting all your historical alt text at once. Prioritize: pages that already get impressions in Google Images (check Search Console, filter by Image search type), product and recipe pages, and your top 20 organic pages. The long tail can wait.

A 30-minute image SEO routine

For each new post or product page, the whole discipline compresses to this:

Resize and compress images before upload; make the hero at least 1200px wide.
Rename files descriptively in kebab-case before uploading.
Write alt text as you insert each image: specific, 8–15 words, keyword only if honest, empty alt for decoration.
Add a caption where a human would benefit.
Confirm the page template emits schema with the featured image, once per template type.

None of these steps is clever. That is rather the point: image SEO is not a trick, it is a labeling discipline. Search engines are still, after all these years, mostly blind — and the sites that describe their images clearly, consistently, and honestly are the ones that get found by them. Do the boring work at upload time and it never needs doing again.

Photo: Atlantic Ambience on Pexels