gemini-2.5-flash-image (image edit) - GPTProto API Documentation

Gemini’s GPTProto format for the image edit API.

curl  --location --request POST 'https://gptproto.com/api/v3/google/gemini-2.5-flash-image/image-edit' \
--header  'Authorization: Bearer ${GPTPROTO_API_KEY}' \
--header  'Content-Type: application/json' \
--data-raw  '{
    "prompt": "Combine two images, making Obama the main character of the poster, and replace the PLuribus text with GPT PROTO.",
    "images": [
        "https://oss.heyoos.com/2025/11/20/e5cd8678ca164470bcbe51a948eb10f0.png",
        "https://oss.heyoos.com/2025/11/27/b9235ffad28040898b3702826c1731f9.jpg"
    ],
    "output_format": "jpeg"
}'

{
  "error": {
    "message": "Invalid signature",
    "type": "401"
  }
}

Parameters

Parameter	Type	Required	Default	Description
`prompt`	string	✅ Yes	-	Description of the edit to be made to the image(s). Be specific about the desired changes.
`images`	array	✅ Yes	-	Array of image URLs to be edited. Supported MIME types: `image/png`, `image/jpeg`, `image/webp`
`output_format`	string	❌ No	`png`	The format of the output image. Supported formats: `png`, `jpeg`
`size`	string	❌ No	`1:1`	Aspect ratio of the output image. Options: 1:1, 3:2, 2:3, 3:4, 4:3, 4:5, 5:4, 9:16, 16:9, 21:9. The model defaults to matching the output image size to that of your input image, or otherwise generates 1:1 squares.

Image Edit

Response

  {
      "created": 1762156444807,
      "data": [
          {
              "b64_json": "image_base64"
          }
      ],
      "output_format": "png",
      "quality": "high",
      "size": "16:9",
      "usage": {
          "input_tokens": 535,
          "input_tokens_details": {
              "image_tokens": 516,
              "text_tokens": 19
          },
          "output_tokens": 1291,
          "total_tokens": 1826
      }
  }

Adding and removing elements

Provide an image and describe your change. The model will match the original image’s style, lighting, and perspective.

Input	Output

A photorealistic picture of a fluffy ginger cat…	Using the provided image of my cat, please add a small, knitted wizard hat…

Advanced composition: Combining multiple images

Provide multiple images as context to create a new, composite scene. This is perfect for product mockups or creative collages.

Input1	Input2	Output

A professionally shot photo of a blue floral summer dress…	Full-body shot of a woman with her hair in a bun…	Create a professional e-commerce fashion photo…

Best Practices

To elevate your results from good to great, incorporate these professional strategies into your workflow.

Be Hyper-Specific: The more detail you provide, the more control you have. Instead of “fantasy armor,” describe it: “ornate elven plate armor, etched with silver leaf patterns, with a high collar and pauldrons shaped like falcon wings.”
Provide Context and Intent: Explain the purpose of the image. The model’s understanding of context will influence the final output. For example, “Create a logo for a high-end, minimalist skincare brand” will yield better results than just “Create a logo.”
Iterate and Refine: Don’t expect a perfect image on the first try. Use the conversational nature of the model to make small changes. Follow up with prompts like, “That’s great, but can you make the lighting a bit warmer?” or “Keep everything the same, but change the character’s expression to be more serious.”
Use Step-by-Step Instructions: For complex scenes with many elements, break your prompt into steps. “First, create a background of a serene, misty forest at dawn. Then, in the foreground, add a moss-covered ancient stone altar. Finally, place a single, glowing sword on top of the altar.”
Use “Semantic Negative Prompts”: Instead of saying “no cars,” describe the desired scene positively: “an empty, deserted street with no signs of traffic.”
Control the Camera: Use photographic and cinematic language to control the composition. Terms like wide-angle shot, macro shot, low-angle perspective.

Limitations

For best performance, use the following languages: EN, es-MX, ja-JP, zh-CN, hi-IN.
Image generation does not support audio or video inputs.
The model won’t always follow the exact number of image outputs that the user explicitly asks for.
The model works best with up to 3 images as an input.
When generating text for an image, Gemini works best if you first generate the text and then ask for an image with the text.
Uploading images of children is not currently supported in EEA, CH, and UK.

API Reference

​Parameters

​Image Edit

​Response

​Adding and removing elements

​Advanced composition: Combining multiple images

​Best Practices