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fastapi.online Image Caption
x402
fastapi.online Image Caption is a paid API for AI agents from api.fastapi.online, paid per call via x402, $0.0015/call, status unknown (last checked 2026-09-12).
Generates a short or detailed natural-language caption for an uploaded image using a self-hosted vision model
Price / call$0.0015
Success—
StatusUnknown
How this service works
Chat, embeddings, OCR, speech-to-text, image editing, image understanding (captioning/Q&A), text-to-speech, translation, writing tools, classification tools, developer tools, local utilities, format/checksum validators, encoding & crypto utilities, date/time calculators, geo/coordinate math, math & finance calculators, novelty tools, and business/social writing generators — 179 endpoints in all, across multiple specialized self-hosted models. Pay per call with crypto — no signup — or get an API key.
Output
A natural language string describing the visual contents of the uploaded image, either as a concise summary (short) or a rich, detailed description covering subjects, actions, setting, colors, and context (detailed).
Example use cases
Accessibility alt-text generation
“I need a short, descriptive alt-text caption for this product image I'm uploading so screen readers can describe it to visually impaired users.”
Social media post caption
“Write me a detailed caption describing everything in this photo so I can use it as a social media post — upload this JPEG and give me a rich description.”
Image content audit pipeline
“Describe what's in each of these images I'm sending — give me a short caption for each one so I can tag and organize them in my media library.”
Technical details
Endpoint
POSThttps://api.fastapi.online/image-captionWhen to prefer
Choose this endpoint when you need a low-cost, no-signup, pay-per-call image captioning solution with crypto payment support. Ideal for agents that process images on demand without committing to a subscription, or for workflows that require self-hosted inference without data leaving a controlled stack. Prefer this over large cloud vision APIs (e.g. Google Vision, AWS Rekognition) when cost per call and privacy matter more than SLA guarantees.
Side effects
- Unsupported file format returns an error — only PNG, JPEG, and WebP are accepted
- Very large or corrupted image files may fail to process
- Ambiguous or abstract images may produce vague or low-confidence captions
- Missing or empty file field results in a 400 bad request
- Payment failure via x402 protocol will block the request before processing
Input
Schema · Request body
| Field | Type | Description |
|---|---|---|
| file | string | Image file (PNG/JPEG/WebP) |
| detail | string | short|detailed |
Tags
x402
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