Image Caption API

POST

Generate alt text and descriptions for any uploaded image.

Image Caption generates natural language descriptions for uploaded image files. Upload a JPG, PNG, or GIF up to 5MB to receive an automated caption for alt text and media tagging.

Try it — live request, no key required

Request

POSTapi.apiverve.com/v1/imagecaption

image

Click or drag a file to upload.jpg, .jpeg, .png, .gif · max 400KB for live testing

Verification

Format

No key required to try it. Get a key to use it in your app.

Example

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

Start from a template — a working app you can deploy in a minute

Image Caption Generator

Upload an image and get a one-sentence description, for alt text, tagging or search.

React
Vite

Deploy to Vercel See the template →

About the Image Caption API

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

What people use it for

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

Ways to call it

One endpoint, many ways in — REST with JSON, XML, YAML and CSV, plus GraphQL and an MCP interface for AI agents.

JSON: Default REST response
XML: Markup format
YAML: Human-readable
CSV: Tabular export
GraphQL: Query language
MCP: For AI agents

View all integrations →

Questions.

Common questions about the Image Caption API.

Read the docs →

Which image formats can I send for captioning?

JPG, JPEG, PNG, and GIF formats are fully supported. Uploads must be sent as an image file through the API's image parameter.

What is the maximum file size for uploaded images?

5MB per image. Any file at or below 5MB in a supported format will be accepted for caption generation.

Do I need to resize high-resolution images before uploading?

No. The Image Caption API automatically resizes images internally for processing. You can send original image files directly as long as they stay under the 5MB limit.

Can I use the generated descriptions as alt text for accessibility?

Yes. The endpoint returns a natural language description of the visual contents of the image. This text is well-suited for automated accessibility alt text, search indexing, and content tagging.

Which plan fits 5,000 image captions a month?

Starter covers this volume easily. Each request uses 20 credits, meaning Starter gives you up to 10,000 captions per month, which works out to about $0.003 per call or $3.00 per 1,000 images. The Free plan includes 10 captions monthly for testing.

Request parameters — POST /v1/imagecaption

Sent as JSON in the request body. Premium parameters are accepted on every plan but only take effect on plans that include them. Anything not listed here is dropped rather than passed through.

Required

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

Example request

curl -X POST "https://api.apiverve.com/v1/imagecaption" \
  -H "x-api-key: YOUR_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{}'

Authentication

Send your key in the x-api-key header. That is the only auth step — no token exchange, and no per-endpoint scope to configure.

Header	When	Value
`x-api-key`Required	Every request	Your API key. Header names are case-insensitive, so `X-API-Key` is the same header.
`Authorization`Alternate	Instead of the above	`Bearer <key>` — for clients that only expose bearer auth. Resolves to the same account and the same billing.
`content-type`Required	POST body	`application/json`

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.

Response — POST /v1/imagecaption

Every APIVerve endpoint returns the same three top-level keys, so one response handler covers your whole integration: status, error and data. Only data changes shape.

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

Response headers

Every response carries your balance, so your own code always knows where it stands without polling anything. All four are exposed to browsers through CORS.

Header	What it carries
`x-api-remaining-credits`	Credits left in the current cycle
`x-api-credits-used`	Credits spent in the current cycle
`x-api-max-credits`	The allowance for the cycle
`x-api-version`	Version of the endpoint that answered

Errors

Read the HTTP status first, then error for the specific reason. The body names the parameter that has to change.

Status	Meaning	What to do
`400`	Input was rejected	Read `error`; it names the parameter that has to change.
`401`	Key missing or invalid	Check the header name and the key value.
`403`	Key valid, but not permitted here	A key restriction or an IP allow-list — never a bad key.
`429`	Rate limited, or out of credits	Read `error` to tell them apart, then back off or top up.

What a call costs — 20 credits per call

Credits are shared across every APIVerve API — one balance, one key, one bill. Failed requests never count against it, so a rejected input costs nothing.

Plan	Per month	Credits	Image Caption calls	Per 1,000 calls
Free	Free	200	10	Free
Starter	$29.99	200,000	10,000	$3.00
Pro	$99.99	1,000,000	50,000	$2.00
Mega	$299.99	4,000,000	200,000	$1.50

Calls are what the credits buy at this API's rate — spend them here, on any of the other APIs, or across both. Nothing is reserved per endpoint.

Compare all pricing tiers →

Call it from cURL — POST /v1/imagecaption

No SDK to install — this is a plain HTTPS call to /v1/imagecaption with your key in the x-api-key header. Swap in a real key and it runs as-is.

cURL

1
2

curl "https://api.apiverve.com/v1/imagecaption" \
  -H "x-api-key: YOUR_API_KEY"

Resources

GitHubapiverve/imagecaption-apiSource, issues and the examples this page is built from.ReferenceImage Caption API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/imagecaptionnpm apiverve-imagecaptionPyPI APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Node.js — POST /v1/imagecaption

Install the Node.js SDK, then call the Image Caption API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — npm

npm install @apiverve/imagecaption

Node.js

const res = await fetch("https://api.apiverve.com/v1/imagecaption", {
  headers: { "x-api-key": "YOUR_API_KEY" },
});
const { data } = await res.json();
console.log(data);

Resources

npm@apiverve/imagecaptionThe published Node.js client, versioned and signed.GitHubapiverve/imagecaption-apiSource, issues and the examples this page is built from.ReferenceImage Caption API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

apiverve-imagecaptionPyPI APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Python — POST /v1/imagecaption

Install the Python SDK, then call the Image Caption API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — PyPI

pip install apiverve-imagecaption

Python

import requests

res = requests.get(
    "https://api.apiverve.com/v1/imagecaption",
    headers={"x-api-key": "YOUR_API_KEY"},
)
print(res.json()["data"])

Resources

PyPIapiverve-imagecaptionThe published Python client, versioned and signed.GitHubapiverve/imagecaption-apiSource, issues and the examples this page is built from.ReferenceImage Caption API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/imagecaptionnpm APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from C# / .NET — POST /v1/imagecaption

Install the C# / .NET SDK, then call the Image Caption API with your key. The client wraps the same HTTPS request, so anything it returns is what the endpoint returns.

Install — NuGet

dotnet add package APIVerve.API.ImageCaption

C# / .NET

using var client = new HttpClient();
client.DefaultRequestHeaders.Add("x-api-key", "YOUR_API_KEY");

var json = await client.GetStringAsync("https://api.apiverve.com/v1/imagecaption");
Console.WriteLine(json);

Resources

NuGetAPIVerve.API.ImageCaptionThe published C# / .NET client, versioned and signed.GitHubapiverve/imagecaption-apiSource, issues and the examples this page is built from.ReferenceImage Caption API docsEvery parameter, every response field, and the errors.ParametersWhat this call acceptsRequired and optional inputs, with example values.

Also published for

@apiverve/imagecaptionnpm apiverve-imagecaptionPyPI

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Go — POST /v1/imagecaption

No SDK to install — this is a plain HTTPS call to /v1/imagecaption with your key in the x-api-key header. Swap in a real key and it runs as-is.

req, _ := http.NewRequest("GET", "https://api.apiverve.com/v1/imagecaption", nil)
req.Header.Set("x-api-key", "YOUR_API_KEY")

res, _ := http.DefaultClient.Do(req)
defer res.Body.Close()
body, _ := io.ReadAll(res.Body)
fmt.Println(string(body))

Resources

Also published for

@apiverve/imagecaptionnpm apiverve-imagecaptionPyPI APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from PHP — POST /v1/imagecaption

No SDK to install — this is a plain HTTPS call to /v1/imagecaption with your key in the x-api-key header. Swap in a real key and it runs as-is.

PHP

$ch = curl_init("https://api.apiverve.com/v1/imagecaption");
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_HTTPHEADER, ["x-api-key: YOUR_API_KEY"]);

$response = curl_exec($ch);
echo $response;

Resources

Also published for

@apiverve/imagecaptionnpm apiverve-imagecaptionPyPI APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

Call it from Ruby — POST /v1/imagecaption

No SDK to install — this is a plain HTTPS call to /v1/imagecaption with your key in the x-api-key header. Swap in a real key and it runs as-is.

Ruby

require "net/http"

uri = URI("https://api.apiverve.com/v1/imagecaption")
req = Net::HTTP::Get.new(uri)
req["x-api-key"] = "YOUR_API_KEY"

res = Net::HTTP.start(uri.hostname, uri.port, use_ssl: true) { |h| h.request(req) }
puts res.body

Resources

Also published for

@apiverve/imagecaptionnpm apiverve-imagecaptionPyPI APIVerve.API.ImageCaptionNuGet

Only the languages APIVerve ships a client for are listed — the rest call the endpoint directly over HTTPS.

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Image Caption API

Try it — live request, no key required

Start from a template — a working app you can deploy in a minute

Image Caption Generator

About the Image Caption API

What people use it for

Ways to call it

Questions.

Request parameters — POST /v1/imagecaption

Required

Authentication

Response — POST /v1/imagecaption

Response fields

Response headers

Errors

What a call costs — 20 credits per call

Call it from cURL — POST /v1/imagecaption

Resources

Also published for

Call it from Node.js — POST /v1/imagecaption

Resources

Also published for

Call it from Python — POST /v1/imagecaption

Resources

Also published for

Call it from C# / .NET — POST /v1/imagecaption

Resources

Also published for

Call it from Go — POST /v1/imagecaption

Resources

Also published for

Call it from PHP — POST /v1/imagecaption

Resources

Also published for

Call it from Ruby — POST /v1/imagecaption

Resources

Also published for

Zero-code embed — one snippet, no backend

Changelog — Image Caption API

AI/Computer Vision

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