OpenRouter Image Inputs - Complete Documentation

Requests with images, to multimodal models, are available via the Responses API (/api/v1/responses) with a multi-part message in the input parameter. Each image is an input_image content part whose image_url can either be a URL or a base64-encoded data URL. Note that multiple images can be sent in separate content array entries. The number of images you can send in a single request varies per provider and per model. Due to how the content is parsed, we recommend sending the text prompt first, then the images. If the images must come first, put them before the text within the same user message; system messages should contain text only. OpenRouter supports both direct URLs and base64-encoded data for images:

URLs: More efficient for publicly accessible images as they don’t require local encoding
Base64: Required for local files or private images that aren’t publicly accessible

Using Image URLs

Here’s how to send an image using a URL:

import { OpenRouter } from '@openrouter/sdk';

const openRouter = new OpenRouter({
  apiKey: '<OPENROUTER_API_KEY>',
});

const result = await openRouter.responses.send({
  responsesRequest: {
    model: 'google/gemini-3-flash-preview',
    input: [
      {
        role: 'user',
        content: [
          {
            type: 'input_text',
            text: "What's in this image?",
          },
          {
            type: 'input_image',
            imageUrl: 'https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg',
            detail: 'auto',
          },
        ],
      },
    ],
    stream: false,
  },
});

console.log(result);

import requests
import json

url = "https://openrouter.ai/api/v1/responses"
headers = {
    "Authorization": f"Bearer {API_KEY_REF}",
    "Content-Type": "application/json"
}

input_items = [
    {
        "role": "user",
        "content": [
            {
                "type": "input_text",
                "text": "What's in this image?"
            },
            {
                "type": "input_image",
                "image_url": "https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg",
                "detail": "auto"
            }
        ]
    }
]

payload = {
    "model": "google/gemini-3-flash-preview",
    "input": input_items
}

response = requests.post(url, headers=headers, json=payload)
print(response.json())

const response = await fetch('https://openrouter.ai/api/v1/responses', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${API_KEY_REF}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    model: 'google/gemini-3-flash-preview',
    input: [
      {
        role: 'user',
        content: [
          {
            type: 'input_text',
            text: "What's in this image?",
          },
          {
            type: 'input_image',
            image_url: 'https://upload.wikimedia.org/wikipedia/commons/thumb/d/dd/Gfp-wisconsin-madison-the-nature-boardwalk.jpg/2560px-Gfp-wisconsin-madison-the-nature-boardwalk.jpg',
            detail: 'auto',
          },
        ],
      },
    ],
  }),
});

const data = await response.json();
console.log(data);

Using Base64 Encoded Images

For locally stored images, you can send them using base64 encoding. Here’s how to do it:

import { OpenRouter } from '@openrouter/sdk';
import * as fs from 'fs';

const openRouter = new OpenRouter({
  apiKey: '<OPENROUTER_API_KEY>',
});

async function encodeImageToBase64(imagePath: string): Promise<string> {
  const imageBuffer = await fs.promises.readFile(imagePath);
  const base64Image = imageBuffer.toString('base64');
  return `data:image/jpeg;base64,${base64Image}`;
}

// Read and encode the image
const imagePath = 'path/to/your/image.jpg';
const base64Image = await encodeImageToBase64(imagePath);

const result = await openRouter.responses.send({
  responsesRequest: {
    model: 'google/gemini-3-flash-preview',
    input: [
      {
        role: 'user',
        content: [
          {
            type: 'input_text',
            text: "What's in this image?",
          },
          {
            type: 'input_image',
            imageUrl: base64Image,
            detail: 'auto',
          },
        ],
      },
    ],
    stream: false,
  },
});

console.log(result);

import requests
import json
import base64
from pathlib import Path

def encode_image_to_base64(image_path):
    with open(image_path, "rb") as image_file:
        return base64.b64encode(image_file.read()).decode('utf-8')

url = "https://openrouter.ai/api/v1/responses"
headers = {
    "Authorization": f"Bearer {API_KEY_REF}",
    "Content-Type": "application/json"
}

# Read and encode the image
image_path = "path/to/your/image.jpg"
base64_image = encode_image_to_base64(image_path)
data_url = f"data:image/jpeg;base64,{base64_image}"

input_items = [
    {
        "role": "user",
        "content": [
            {
                "type": "input_text",
                "text": "What's in this image?"
            },
            {
                "type": "input_image",
                "image_url": data_url,
                "detail": "auto"
            }
        ]
    }
]

payload = {
    "model": "google/gemini-3-flash-preview",
    "input": input_items
}

response = requests.post(url, headers=headers, json=payload)
print(response.json())

import * as fs from 'fs';

async function encodeImageToBase64(imagePath: string): Promise<string> {
  const imageBuffer = await fs.promises.readFile(imagePath);
  const base64Image = imageBuffer.toString('base64');
  return `data:image/jpeg;base64,${base64Image}`;
}

// Read and encode the image
const imagePath = 'path/to/your/image.jpg';
const base64Image = await encodeImageToBase64(imagePath);

const response = await fetch('https://openrouter.ai/api/v1/responses', {
  method: 'POST',
  headers: {
    Authorization: `Bearer ${API_KEY_REF}`,
    'Content-Type': 'application/json',
  },
  body: JSON.stringify({
    model: 'google/gemini-3-flash-preview',
    input: [
      {
        role: 'user',
        content: [
          {
            type: 'input_text',
            text: "What's in this image?",
          },
          {
            type: 'input_image',
            image_url: base64Image,
            detail: 'auto',
          },
        ],
      },
    ],
  }),
});

const data = await response.json();
console.log(data);

Supported image content types are:

image/png
image/jpeg
image/webp
image/gif

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Image Inputs

Using Image URLs

Using Base64 Encoded Images

​Using Image URLs

​Using Base64 Encoded Images

Using Image URLs

Using Base64 Encoded Images