AI Image Caption Generator: Auto Alt Text for Accessibility & SEO

Every image on the web should carry a short text description. Screen readers announce it to people who cannot see the picture, search engines read it to understand what the page is about, and browsers fall back to it when an image fails to load. That text is called alt text, and writing it well for hundreds of images is one of the most tedious jobs in web publishing. An AI image caption generator takes the first draft off your plate. The BrowseryTools Image Captioner turns any photo into a descriptive caption and a ready-to-paste alt="…" snippet — entirely in your browser, with no upload.

Caption vs. Alt Text — Why You Need Both

People use the words interchangeably, but they do different jobs. A caption is visible text shown next to an image — a figure label, a product line, a social-media description. Alt text is the hidden alt attribute on an <img> tag. It is read aloud by assistive technology and indexed by search engines, but it does not appear on the page unless the image breaks. The good news is that a single descriptive sentence usually works for both, which is why this tool produces one caption and then wraps it as a copy-ready alt attribute.

How the AI Generates a Caption

Under the hood the tool runs an image-to-text model called vit-gpt2-image-captioning. It pairs a Vision Transformer, which encodes the picture into a numeric representation of what it contains, with a GPT-2 language head that turns that representation into an English sentence. The model has seen millions of captioned images, so it has learned to name common objects, scenes, and actions — "a dog running on a beach", "a plate of food on a table", "a person riding a bike". You upload an image, the model runs, and a few seconds later you get a sentence describing it.

It Runs On Your Device — Nothing Is Uploaded

This is the part that sets BrowseryTools apart. The model is fetched once from a public CDN and then cached in your browser. From that point on, every caption is generated locally using WebGPU when your browser supports it, or WebAssembly as a fallback. Your image never leaves your computer. There is no server, no account, and no usage limit — which matters when you are captioning client photos, internal screenshots, or anything you would rather not send to a third-party API.

Why Alt Text Matters for Accessibility

Roughly one in twenty people browse with some form of visual impairment. For them, a screen reader is the page. An image with no alt text is announced as just "image" or, worse, read out as a meaningless file name like IMG_4821.jpg. Good alt text closes that gap. The Web Content Accessibility Guidelines (WCAG) require a text alternative for every non-decorative image, and providing one is also a legal requirement in many jurisdictions. Generating a solid first draft for every image makes compliance realistic instead of aspirational.

Why Alt Text Matters for SEO

Search engines cannot see pixels, so they lean on alt text to understand and rank images. Descriptive alt attributes help your photos surface in Google Images, add relevant keywords in context, and strengthen the topical signal of the whole page. An alt text generator for accessibility and SEO like this one lets you ship descriptive attributes at scale instead of leaving them blank — which is the single most common image-SEO mistake.

Always Review the Output

AI captions are a starting point, not a final answer. The model describes what it sees literally; it does not know your context. For a product photo it might say "a pair of shoes" when you need "Nike Air Zoom Pegasus 40 in volt green". For a chart it will not read the data. So treat the generated caption as a fast first draft: keep it under about 125 characters, add the specifics the model cannot know, and drop phrases like "image of" since the context already implies it. For purely decorative images, use an empty alt="" so screen readers skip them.

A Simple Workflow

1. Drop an image onto the tool.
2. Click Generate caption and wait for the model.
3. Read the caption and copy it, or copy the ready-made alt="…" snippet.
4. Paste it into your CMS or HTML, then edit in the specifics only you know.

Private, Free, and Built for Real Work

Whether you are making a blog accessible, captioning a product catalog, or adding alt text to documentation, an on-device AI image caption generator turns a dreaded chore into a few clicks. Try it now with the Image Captioner & Alt Text Generator — no upload, no account, no limits.