feat: add Image type for image-specific file handling

[zeke]

This experimental PR adds a new cog.Image type that extends cog.Path to provide image-specific handling in model inputs and outputs.

The Image type works identically to Path but produces OpenAPI schemas with format: "uri" and x-cog-type: "image", following the same pattern as streaming outputs that use x-cog-array-type: "iterator". This allows UIs to provide image-specific widgets while correctly identifying the value as a URI.

Example usage

from cog import BasePredictor, Input, Image
import tempfile

class Predictor(BasePredictor):
    def predict(self, image: Image = Input(description="Input image")) -> Image:
        processed_image = do_some_processing(image)
        
        output_path = Image(tempfile.mkdtemp()) / "processed.png"
        processed_image.save(output_path)
        return Image(output_path)

OpenAPI schema

The generated OpenAPI schema for an Image input:

{
  "image": {
    "title": "Image",
    "description": "An input image",
    "type": "string",
    "format": "uri",
    "x-cog-type": "image"
  }
}

Related:

• Add an image mask file type #2014
• Let model authors specify filetypes for inputs and outputs (audio, video, image, etc) #1341