Image Captioner
Generate captions for images with AI
Click or drop an image hereChoose an image
Max 80 MB per image — it is reduced on your device before sending, so large photos work
About Image Captioner
Image Captioner writes a short, descriptive caption for a photo or picture, using OpenAI's GPT-4o mini vision model. You pick one image of up to 80 MB: JPG, PNG, and WebP open in every browser, and a HEIC photo opens in Safari. Before it is sent, the page turns it on your device into a JPG of at most 2,048 pixels on the longest side; only that copy goes through our server to OpenAI. The caption is plain text to copy or download as caption.txt. Transparent areas are sent as white, and one image is captioned at a time.
How to generate a caption for an image
- 1Click the upload area and choose an image; a preview appears.
- 2Click "Generate caption" and wait while it shows "Generating…".
- 3Read the text under "Caption".
- 4Click "Copy" or "Download" (caption.txt) to keep it.
Formats and limits
- Input formats
- Any image your browser can decode, such as JPG, PNG, or WebP
- Maximum size
- 80 MB per image
- Sent for analysis
- A JPG copy, 2,048 px at most on the longest side
- Output
- One caption in plain text, with a .txt download
- Usage limits
- A limited number of requests per connection each hour and each day, shared with the site's other tools that rely on a paid service, and a monthly budget for the whole site
Where your image is processed
Before it is sent, your image is redrawn on your device as a JPG with its longest side at 2,048 px or less and any transparency turned white; only that redrawn copy is sent to our server, and your original file stays on your device. Our server passes the copy to OpenAI's GPT-4o mini vision model, which writes the caption. We do not store the image or the caption.
Frequently asked questions
Is my full-size photo uploaded?
No. Only a JPG copy, at most 2,048 pixels on its longest side, leaves your device, and it goes through our server to OpenAI. The original file is read in your browser and is never sent.
Can I use a HEIC photo from an iPhone?
Yes in Safari, which opens HEIC itself; in Chrome, Edge, or Firefox, convert it first with HEIC to JPG. JPG, PNG, and WebP work in every browser, up to 80 MB, and an animated GIF is captioned from a single frame.
Can I use the caption as alt text?
Yes, after checking it. The model is asked for a creative, descriptive caption, so it may add mood or style words that alt text does not need. Trim it to what the image shows and why it matters on your page.
Why was my image refused?
80 MB is the size limit, and an image the browser cannot read is refused too; both are explained before anything goes to our server. A request can also be stopped by your connection's hourly or daily limit or the site's monthly budget, and the message says when to try again.
Tips and tricks
- ✓For a logo with a transparent background, check the caption: transparent areas reach the model as white.