Image Caption API Reference

Overview

Supports common image formats including JPG, PNG, and GIF. Images are automatically resized for optimal processing. Maximum file size is 5MB.

Endpoint

One host, one path per API. The block below shows this call in four languages; every one of them is the same HTTP request. Making requests covers the timeouts, retries and parameter rules that apply to all of them. The SDKs wrap the same call in a typed client.

POSThttps://api.apiverve.com/v1/imagecaption

curl -X POST https://api.apiverve.com/v1/imagecaption \
  -H "x-api-key: your_api_key_here" \
  -H "Content-Type: application/json" \
  -d '{
  "image": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Cat03.jpg/640px-Cat03.jpg"
}'

const res = await fetch('https://api.apiverve.com/v1/imagecaption', {
  method: 'POST',
  headers: {
    'x-api-key': 'your_api_key_here',
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
  "image": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Cat03.jpg/640px-Cat03.jpg"
}),
});

if (!res.ok) throw new Error(`${res.status} ${await res.text()}`);

const { data } = await res.json();
console.log(data);

import requests

res = requests.post(
    "https://api.apiverve.com/v1/imagecaption",
    headers={"x-api-key": "your_api_key_here"},
    json={
    "image": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Cat03.jpg/640px-Cat03.jpg"
},
    timeout=15,
)
res.raise_for_status()

print(res.json()["data"])

package main

import (
	"fmt"
	"io"
	"net/http"
	"strings"
)

func main() {
	body := strings.NewReader(`{
  "image": "https://upload.wikimedia.org/wikipedia/commons/thumb/3/3a/Cat03.jpg/640px-Cat03.jpg"
}`)
	req, _ := http.NewRequest("POST", "https://api.apiverve.com/v1/imagecaption", body)
	req.Header.Set("Content-Type", "application/json")
	req.Header.Set("x-api-key", "your_api_key_here")

	res, err := http.DefaultClient.Do(req)
	if err != nil {
		panic(err)
	}
	defer res.Body.Close()

	out, _ := io.ReadAll(res.Body)
	fmt.Println(string(out))
}

Replace your_api_key_here with the key from your dashboard. When the inputs arrive as a list rather than one at a time, batch requests run up to 200 of them through this same API in a single call.

Authentication

Send your key in the x-api-key header. That is the only auth step — there is no token exchange and no per-endpoint scope to configure. Authentication covers creating, rotating and revoking keys.

401 is the only auth verdict

A 401 means the key is missing, invalid or expired. A 403 means the key is valid but not permitted here — blocked by a key restriction or an IP allow-list. Running out of credits is a 429.

Parameters

Sent as JSON in the request body. Premium parameters are accepted on every plan but only take effect on plans that include them.

Parameter	Type	Description
`image`Required	string	Upload an image file to generate a caption (supported formats: JPG, PNG, GIF, max 5MB)

Response

Every API returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape. Response format covers the envelope, the other output formats and how premium fields are withheld.

Sample response

{
  "status": "ok",
  "error": null,
  "data": {
    "caption": "A golden retriever running through a grassy field on a sunny day"
  }
}

Response fields

Paths are relative to data. Premium fields are absent rather than zeroed on plans that do not include them, so check for presence instead of comparing to 0.

Field	Type	Example	Description
`caption`	string	`"A golden retriever running through a grassy field on a sunny day"`	AI-generated natural language description of image contents

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change. Error handling covers the full status list and which of them are worth retrying.

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted	A key restriction or IP allow-list; see key scoping.
`429`	Rate limited, or out of credits	Read `error` to tell them apart; see rate limits.

Use cases

Accessibility: Generate alt text for images to improve web accessibility for visually impaired users
Content Management: Automatically generate descriptions for large image libraries and media assets
Social Media: Create engaging captions for social media posts and marketing content
Search Optimization: Improve image searchability by generating descriptive metadata

Set up Image Caption

Ready to put it to work? Set up Image Caption on APIVerve.

Image Caption