AI Image Captioner
Generate accurate image captions and alt text using AI that runs entirely in your browser. Your images stay private — nothing is uploaded. Perfect for SEO alt tags, social media captions, and accessibility. Works in all browsers.
Drop an image here or click to upload
Supports JPG, PNG, WebP — max 10MB
How AI Image Captioning Works in Your Browser
This tool uses the ViT-GPT2 image captioning model through Transformers.js. The model combines a Vision Transformer (ViT) that "sees" the image with GPT-2 that generates natural language descriptions. It runs entirely in your browser — your images are never uploaded to any server.
The model was trained on millions of image-caption pairs and can recognize objects, scenes, actions, colors, and spatial relationships. It outputs human-readable captions that describe the most important elements of your photo.
How It Works — Step by Step
- Image encoding: The Vision Transformer processes your image into a feature representation that captures objects, scenes, and layout.
- Text generation: GPT-2 takes those features and generates a natural language caption describing the image.
- Multiple captions: The model generates several candidate captions with confidence scores so you can choose the best one.
- All local: Every step runs in your browser using WebAssembly. Nothing is uploaded.
Use Cases for AI Image Captioning
SEO Alt Text Generation
Search engines rely on alt text to understand images. Use AI-generated captions as a starting point for descriptive, keyword-rich alt tags that improve your page's SEO ranking and image search visibility.
Social Media Captions
Struggling with what to write for your Instagram or Twitter post? Let the AI describe your photo, then edit and personalize the caption. Great for content creators who need ideas fast.
Accessibility Compliance
WCAG accessibility guidelines require descriptive alt text for all meaningful images. This tool helps web developers and content managers quickly generate accurate descriptions for screen readers, making websites accessible to visually impaired users.
Image Organization and Searchability
Generate descriptions for large photo libraries to make them searchable. Useful for photographers, digital asset managers, and media companies managing thousands of images.
Content Writing
Writers and bloggers can use AI captions to quickly describe images in articles. The tool provides a solid first draft that can be refined for tone and context.
Why This Tool Stands Out
Most image captioning services upload your photos to cloud servers. This tool is fundamentally different: the AI model downloads once and runs locally forever. Your personal photos, product images, confidential screenshots — none of it ever leaves your device. There are no accounts, no limits, and no watermarks.