Alt Text Is SEO: Images That Rank

There is a strange asymmetry in how people build websites. They will spend hours choosing the right photograph for a page, cropping it, compressing it, testing it on three screen sizes. Then they will upload it with the filename IMG_4032.jpg and an empty alt attribute, and consider the job done. All that care went into what humans see, and none into what machines see. And machines are half the audience.

Alt text was invented for accessibility. If you use a screen reader, the alt attribute is the image. That alone is reason enough to write it. But there is a second consumer of alt text that most site owners forget about: search engines. A crawler cannot look at your photograph and know it shows a plumber fixing a kitchen sink. Computer vision has gotten good, but search engines still lean heavily on the text you give them, because text is unambiguous and cheap to trust. The alt attribute is you telling the search engine, in plain words, what the image is. Skip it and the image is a blank spot in your page as far as ranking is concerned.

This matters more than people think, for two reasons. The first is image search itself. For some kinds of business, image search is not a novelty; it is where customers actually start. If you sell furniture, or do landscaping, or bake wedding cakes, a meaningful number of your future customers begin by looking at pictures. An image with descriptive alt text, a sensible filename, and relevant surrounding text can rank in image results and pull people to a page that would never have ranked in ordinary web search. That traffic is essentially unclaimed, because so few of your competitors bother.

The second reason is subtler. Alt text is part of the page’s text. It contributes to the search engine’s understanding of what the page is about. A page about repairing vintage bicycles, with six images whose alt texts all describe vintage bicycle repair, is more legibly about that topic than the same page with six silent images. You are not stuffing keywords; you are describing what is actually there. It happens that describing what is actually there is what search engines reward. This is a pattern you see all over SEO: the honest move and the effective move are usually the same move.

So how do you write good alt text? The test I use is the phone test. Imagine reading the page aloud to someone over the phone. When you hit the image, what would you say? You would not say “image” — they know it’s an image. You would not recite keywords. You would say something like “a photo of the finished deck, with the built-in bench along the left side.” That’s the alt text. Specific, short, written for a person. If the image is purely decorative — a swoosh, a background texture — the right move is an empty alt attribute, alt="", which tells screen readers to skip it. Note that an empty alt attribute and a missing alt attribute are different things. Empty means “deliberately nothing here.” Missing means “the author didn’t think about it,” and screen readers may fall back to reading the filename, which is worse than silence.

The most common failure I see is not bad alt text but no alt text. When I run GazeSite scans across small-business sites, missing alt attributes show up so often that it barely registers as a finding anymore; it is closer to the default state of the web. The second most common failure is the opposite vice: alt text written for robots. “Best plumber Austin TX emergency plumbing services affordable” is not a description of an image. Search engines have been trained on decades of this stuff and discount it, and a screen reader user has to sit through it. You have taken a feature meant to help blind people and turned it into spam they are forced to listen to. Don’t do that.

There is one more habit worth mentioning: images of text. People render a headline or a price list as a PNG because they like the typography, and then the words inside it vanish from the page. Screen readers can’t read them, search engines can’t index them, and users can’t select or translate them. If the words matter, put them in HTML and style them with CSS. If you truly must use an image of text, the alt text should contain the same words the image shows.

None of this is hard. Writing alt text for a whole site is an afternoon of work, and it is the kind of work that compounds: it makes the site more accessible, more indexable, and more robust when images fail to load. What makes it interesting to me is what its absence reveals. A site with no alt text is a site built entirely from the sighted visitor’s point of view, by someone who never imagined any other reader — human or machine. The fix is not really a technique. It is a shift in perspective: your page has readers you cannot see, and they deserve the same care as the ones you can.