Fixing Missing or Weak Image Alt Text for Search

What alt text does for search, and what it does not

Google's own image guidance says it uses alt text, together with computer vision and the content of the page, to work out what an image is about. Bing describes a similar approach. That makes alt text one input among several rather than a magic ranking lever, but it is the input you control most directly and the one most often left blank or filled with rubbish.

For search, alt text does three useful jobs:

• It labels the image for image search. A product photo whose alt reads "Oak bedside table with two drawers, natural finish" can match searches for exactly that. One whose alt reads DSC_0412 gives the search engine nothing to match.
• It acts as anchor text when the image is a link. Google's documentation states that when an image is used as a link, its alt text is treated much like the anchor text of a text link. A row of category tiles with empty alt passes no description of the pages they point to.
• It supports the page's own topic. Accurate alt on the images of a page about garden sheds reinforces what that page covers. It will not rescue a thin page, but it removes a gap.

What alt text does not do is rank a page by repetition. Google's spam policies name keyword stuffing, and stuffing alt attributes is still stuffing. A long list of search phrases in an alt attribute is also a poor experience for anyone using a screen reader, which is the audience the attribute was designed for.

The signals read alongside alt text

Improving alt text in isolation leaves most of the value on the table. Search engines combine it with several other clues, and when they agree the image is easier to understand and rank. When they contradict each other, for example a file called blue-kettle.jpg with alt text about a toaster, the signal is muddied.

Of these, the file name is the one that is hardest to change later, because renaming a file changes its URL and any image search visibility built on the old URL starts again. Get names right at upload, and only rename existing images when they are genuinely meaningless.

Finding weak alt text across a whole site

Checking alt text page by page does not scale beyond a small brochure site. Run the Image Optimisation audit on your key templates to see the pattern, then use a crawler to collect every image and its alt attribute across the site into one spreadsheet. Most desktop crawlers, including Screaming Frog SEO Spider and Sitebulb, can export image URLs, the pages they appear on and their alt text.

Once it is in a spreadsheet, sort and filter for these patterns. Each points to a different cause and a different fix.

1. No alt attribute at all on images that clearly carry content, such as product photos, team photos, diagrams and article images.
2. Alt that is a file name or camera code: values matching IMG_, DSC, PXL_, screenshot, .jpg or a string of digits. This usually means a CMS copied the file name into the alt field automatically.
3. The same alt on many different images: sort the alt column and count repeats. A shop where 300 photos all say "product image", or every gallery picture repeats the product name, is the common case.
4. Boilerplate from the theme: alt values like "banner", "slide 1", "hero" or the site name on every page.
5. Stuffed alt: very long values, repeated phrases, lists separated by commas or pipes, or town names tacked on for local search.
6. Empty alt on content images: alt="" is correct for decoration but wrong for a product shot, because it tells every reader, including search engines, that the image has nothing to say.

# Quick check on one page: images with no alt attribute
curl -s https://www.example.co.uk/shop/oak-bedside-table \
  | grep -oiE '<img[^>]*>' | grep -viE 'alt=' | head

# Repeated alt values on the same page, most common first
curl -s https://www.example.co.uk/shop/oak-bedside-table \
  | grep -oiE 'alt="[^"]*"' | sort | uniq -c | sort -rn | head

A shell check like this only sees the HTML the server sends. If the site builds its galleries with JavaScript, use a crawler with JavaScript rendering switched on, or the rendered HTML shown in Search Console's URL Inspection tool, to see what Google actually receives.

Weak alt and better alt, side by side

The aim is to describe what the image shows, in the words a person searching for that thing would use, without writing a keyword list. The examples below are from fictional businesses.

Notice what the better versions have in common. They name the thing and the detail that makes this picture different from the one next to it. They use ordinary words, not search phrases. Where a place or brand genuinely appears in the picture it is fine to name it, but a location added only for search, such as a town name on a photo of a spanner, does not describe the image.

Length

There is no official character limit in HTML or in Google's guidance. In practice a phrase or one short sentence is enough for almost every image. Screen reader users hear the whole value, so long alt text becomes tedious, and anything more than a sentence usually belongs in a caption or the body copy where every visitor can read it.

Galleries of similar images

Product galleries are where duplicate alt text multiplies. Give each image the product name once and then the thing that differs: the angle, the colour, the detail shown, or the product in use. That gives image search several distinct, accurate descriptions rather than one repeated several times.

Images search engines cannot see

Perfect alt text does nothing for an image that search engines never find. Google's documentation says it indexes images from HTML <img> elements, including those inside <picture>, and does not index images set as CSS backgrounds. Several common patterns hide content images from image search:

• Hero and banner images set with background-image. Fine for decoration; a loss if the picture is the product or the work you want found.
• Lazy-load scripts that keep the real address in data-src and put a blank placeholder in src. Native loading="lazy" keeps the real address in src and avoids this.
• Galleries built entirely in JavaScript from a JSON feed, with no image elements in the server HTML. Google can render JavaScript, but relying on it adds delay and risk; server-rendered image elements are safer.
• Images blocked by robots.txt, often because an uploads or media folder was disallowed years ago.
• Images on a separate domain or CDN that blocks crawlers or requires cookies.

The fix, step by step

Where alt text is stored on common platforms

Most alt problems at scale come from how the platform stores and outputs the value rather than from individual editors. Knowing where the value lives tells you where to fix it.

• WordPress. The media library holds an alt value for each attachment. In the block editor the alt is written into the post content when the image is inserted, so changing it later in the media library does not update posts that already use the image. Featured images and many theme and page-builder widgets read the media library value instead. Bulk fixes therefore need both places checked.
• Shopify. Product media has its own alt field in the product admin, and themes normally output it through Liquid. Images in theme sections take their alt from the file in the Files area. Some older themes print the product title instead of the stored alt, which produces identical alt across a gallery.
• Headless and custom systems. Check the content model. If the image field has no alt property, editors cannot add one, and the front end will fall back to a title or nothing. Add an alt field to the asset or the reference, and make it required for content images.
• Page builders. Image widgets often have their own alt box that overrides the library, or an option to use the title. Check the widget settings used most on your key templates.

Automatic alt text

Several platforms and plugins can now suggest alt text using image recognition. These suggestions are a reasonable starting point for large back catalogues, but they describe what is visible, not why it matters on this page. They cannot know that a photo shows your own bespoke kitchen rather than a kitchen, or that the important detail is the dovetail joint. Review suggestions before publishing, starting with the pages that earn the most traffic.

Edge cases

• Multilingual sites. Alt text should be translated with the page. An English alt on a French page is a mismatch for both readers and search engines. Check that the translation tool includes image attributes.
• Logos. A linked logo in the header needs alt that names the business, because it acts as a link, typically to the home page. There is no search benefit in adding a slogan or keywords to it.
• Text inside images. If a graphic contains words that matter, such as an offer or a quote, put those words in the alt and preferably in real HTML text too. Text baked into pixels is a weak signal even with character recognition.
• Stock photos. Alt text on a generic stock photo will not make it rank well, because the same picture appears on many other sites. Original photographs of your own products, premises and work have far more to gain from good alt text.
• SVG. An SVG loaded with an <img> tag takes alt like any other image. Inline SVG does not have an alt attribute; if it carries meaning, give it a title or an accessible label instead.

Keeping alt text good as the site grows

• Make alt a required field for content images in the CMS or product import, with a clear way to mark a genuinely decorative image instead.
• Turn off file-name-to-alt copying in upload settings and plugins.
• Add alt columns to product imports so bulk uploads arrive with descriptions rather than blanks.
• Write a short house style: name the thing, then the distinguishing detail, one sentence, no keyword lists, translated with the page.
• Re-crawl quarterly and filter for the same patterns: missing, file-name, duplicate and overlong alt.

For how images fit into the rest of the audit, see the Image Optimisation Guide. For product galleries specifically, the product images guide covers variants and feeds.