Your Media Library Is Full of Missing Alt Text. Here's What It Costs You

On most sites that have been running for a few years, the majority of images have no alt text at all. The first cost is the one that matters: every screen-reader user hits an unlabelled image and gets nothing. The second is that search engines lose the only description of that image they were ever going to get.

Alt text is a written description of an image that screen readers speak aloud to blind and low-vision users, browsers display when an image fails to load, and search engines read to understand what an image shows. Written well, it serves accessibility first and search second: describe what the image shows or does in one specific sentence, skip filler like "image of," and leave purely decorative images with empty alt attributes. The SEO benefit is real but should be stated honestly: alt text helps images rank in image search and adds context to the page, and it is one of many signals rather than a magic ranking key. This guide covers how to write alt text properly, when to leave it empty, what SEO gains to actually expect, and how to clear an alt text backlog across a whole media library without lowering the quality bar.

Alt text serves screen-reader users first

Before alt text was an SEO checkbox, it was, and remains, an accessibility requirement. When a screen reader reaches an image, it reads the alt text aloud. That sentence is the image for the listener. If the alt text is missing, many screen readers fall back to reading the filename, so the user hears "IMG underscore 4 7 3 2 dot jpeg" where sighted users see a chart that carries the argument of the whole section.

This ordering of priorities is not just ethics; it is also the best writing instruction you will get. Alt text written to genuinely stand in for the image, for a person who cannot see it, is almost always exactly what search engines want too: specific, descriptive, honest. Alt text written for a crawler first tends toward keyword lists that fail both audiences. Write for the listener, and the crawler is served for free.

Web accessibility guidelines (WCAG) require text alternatives for meaningful images, and in a growing number of jurisdictions that is a legal compliance matter for many organizations, not a nice-to-have.

How to write good alt text

Describe content or function, whichever the image is doing

Images do one of two jobs, and the alt text should match the job:

• Content images convey information. Describe what they show: not "chart" but "line chart showing organic traffic rising steadily from January to June after the site migration."
• Functional images do something. When an image is a link or a button, describe the function, not the pixels: an image of a magnifying glass that submits a search should be "Search," not "magnifying glass."

Be specific, be brief

Aim for one focused sentence, roughly 125 characters as a soft guide, since some screen readers historically chunk longer descriptions awkwardly. Specificity beats length:

• Weak: dog
• Better: golden retriever
• Good: Golden retriever catching a frisbee mid-jump on a beach

Include detail up to the point where it stops helping someone understand why the image is on this page, and stop there. A product photo's alt text should identify the product and the variant shown; it does not need the studio lighting described.

Skip "image of" and "picture of"

Screen readers already announce images as images. "Image of a golden retriever" makes the listener hear "image, image of a golden retriever." Start with the subject.

Use keywords only where they are the honest description

If the page targets "standing desk setup" and the photo genuinely shows a standing desk setup, then the phrase belongs in the alt text because it is simply accurate. What never belongs is stuffing: standing desk, best standing desk, standing desk setup, ergonomic desk describes nothing and is the one alt text pattern that can actively hurt, since it reads as spam to search engines and as noise to listeners.

Context changes the right answer

The same photo needs different alt text on different pages. On a product page, the team photo caption might be "the founding team"; in a news post about a funding round, "Co-founders Ana Ruiz and David Chen signing the Series A agreement" (an invented illustration) is the version that serves the page. Alt text is page copy, not image metadata.

Decorative images: empty alt is correct alt

Not every image deserves a description. Purely decorative images (background flourishes, divider graphics, an abstract shape that adds visual rhythm and zero information) should carry an empty alt attribute: alt="". That is not the same as a missing attribute. Empty alt explicitly tells screen readers "skip this, nothing here," which is a kindness; a missing attribute forces the filename fallback, which is noise.

The test: if the image vanished, would a reader lose any information or function? No loss means decorative, means alt="". Never write filler like "decorative border graphic"; that forces every screen-reader user to listen to your decoration.

What alt text honestly does for SEO

Stated without inflation:

• Image search. Alt text is a primary way search engines understand what an image depicts, so descriptive alt text is close to a prerequisite for ranking in image results. For sites whose content is visual (products, recipes, tutorials, portfolios), image search is a genuine traffic source worth competing in.
• Page context. Alt text is on-page text that reinforces what the page covers. It contributes context; it does not carry a page by itself.
• Resilience. When images fail to load, alt text keeps the page comprehensible, which quietly protects the experience your rankings ultimately depend on.

What it does not do: rescue thin content, substitute for real page copy, or reward keyword repetition. Alt text is one signal among many, and its discovery-side twin is making sure the images themselves are found, which is where image entries in your XML sitemap come in; Hydrogen SEO includes them in its sitemaps automatically.

Auditing a media library (the honest state of most sites)

Almost every WordPress site more than a year old has an alt text debt: hundreds or thousands of images uploaded in a hurry, alt fields blank, filenames like final-final-v3.png. Fixing it starts with seeing it.

Hydrogen SEO's on-page SEO analysis checks images in the post you are editing, so new content stops adding to the debt, and site audits surface issues across the site so you can size the backlog instead of guessing at it. Prioritize like this:

1. Money pages first. Product images, service pages, your most-trafficked posts.
2. Content images before decorative. Charts, screenshots, and product photos carry information; fix those, and mark true decoration as empty-alt.
3. The archive last, in bulk. Which brings us to the practical question.

Bulk AI alt text, with review

Writing a thousand alt descriptions by hand is the task that never leaves the to-do list. Hydrogen SEO's image alt text tools use AI to describe what an image actually shows, either one image at a time in the editor or in bulk across the entire media library, with a free account connected.

The workflow that keeps quality honest:

1. Run bulk generation across the library. The AI looks at each image and drafts a description of its visible content.
2. Review before you rely. AI drafts are strong on literal content ("person typing on a laptop at a wooden desk") and blind to your context (that this laptop screenshot specifically shows the settings screen your tutorial references). Skim the drafts; correct the ones on important pages; accept the rest as a vast upgrade over silence.
3. Handle function yourself. AI describing pixels cannot know an image is a link whose alt should say where it goes. Functional images need the human pass.
4. Mark decorative images as decorative rather than accepting a generated description of your divider swirl.

If you prefer delegating conversationally, Hydrogen AI, the agent in the plugin dashboard, works through the plugin's registered abilities with plain-language instructions, shows every change, and asks before writing by default, so the review step is built into the interaction rather than bolted on.

Ten minutes of review on top of an automated pass gets a site from "mostly silent images" to "described, with the important ones described well." That is the realistic gold standard, and it is very reachable.

Describe what matters

Alt text is a rare SEO task where doing the right thing for people and doing the right thing for rankings are the same act. Describe content, state function, empty-alt the decoration, skip "image of," and let honest descriptions do their modest, real work in image search.

The Hydrogen SEO plugin is free, and its audits will show you your alt text debt today. Create a free account to unlock single and bulk AI alt text, and clear a year of backlog in an afternoon, with your judgment in the loop.