# Image Captioner by PDF Extract API

> Image Captioner by PDF Extract API is a paid API for AI agents from image-captioner.pdfextractapi.workers.dev, paid per call via x402, $0.02/call, status unknown (last checked 2026-09-15).

Analyzes an uploaded image and returns a human-readable caption, alt text, descriptive tags, and dominant colors.

## Facts

- Endpoint: POST https://image-captioner.pdfextractapi.workers.dev/caption
- Price: $0.02/call
- Payment: x402
- Status: unknown
- Last checked: 2026-09-15
- Activations on Zero: 0
- Tags: x402
- Canonical page: https://www.zero.xyz/c/image-captioner-by-pdf-extract-api-e5f723a7
- Structured record (JSON): https://api.zero.xyz/v1/capabilities/cap_Vx8CckF1wJ3J1OsSl1JOL

Status and success rate cover calls made through Zero and Zero's own probes. Third-party monitors may report differently.

## How to call it through Zero

Zero handles the 402 payment challenge and records the run. With the Zero CLI installed (`npm i -g @zeroxyz/cli`):

```sh
zero fetch --capability image-captioner-by-pdf-extract-api-e5f723a7 -d '<json body>'
```

Example prompt: Can you analyze this image file and give me a caption, alt text, a list of descriptive tags, and the dominant colors in it?

## When to prefer this

Choose this endpoint when you need to enrich image assets with metadata — especially caption text, accessibility alt text, content tags, and color palette — in a single call without setting up your own vision model pipeline. It is well-suited for content management, e-commerce cataloging, and accessibility workflows where you need structured image descriptions quickly and cheaply at $0.02 per image.

## Known failure modes

- Missing or malformed image file returns an error — file field is required
- Unsupported image format may cause processing failure
- Large file sizes may exceed Cloudflare Worker limits and result in a timeout or error
- Invalid body type (not form-data with binary file) causes schema validation failure
- Network timeout if image processing takes too long

## How this service works

Generate a caption, alt text, tags, and dominant colors for an image.

## Output

The endpoint returns a structured response containing a generated natural-language caption describing the image, alt text suitable for accessibility use, a list of descriptive tags, and the dominant colors present in the image.

## Request schema (JSON Schema)

```json
{
 "type": "object",
 "$schema": "https://json-schema.org/draft/2020-12/schema",
 "required": [
  "input"
 ],
 "properties": {
  "input": {
   "type": "object",
   "required": [
    "type",
    "method",
    "bodyType",
    "body"
   ],
   "properties": {
    "body": {
     "required": [
      "file"
     ],
     "properties": {
      "file": {
       "type": "string",
       "format": "binary"
      }
     }
    },
    "type": {
     "type": "string",
     "const": "http"
    },
    "method": {
     "enum": [
      "POST"
     ],
     "type": "string"
    },
    "bodyType": {
     "enum": [
      "json",
      "form-data",
      "text"
     ],
     "type": "string"
    }
   },
   "additionalProperties": false
  },
  "output": {
   "type": "object",
   "required": [
    "type"
   ],
   "properties": {
    "type": {
     "type": "string"
    },
    "example": {
     "type": "object"
    }
   }
  }
 }
}
```

## More

- Live health (JSON, refreshed every minute): https://www.zero.xyz/c/image-captioner-by-pdf-extract-api-e5f723a7/health.json
- [Zero catalog index](https://www.zero.xyz/llms.txt)
- [Other services from image-captioner.pdfextractapi.workers.dev](https://www.zero.xyz/host/image-captioner.pdfextractapi.workers.dev/llms.txt)