[Bug] dspy.Image not actually leading to generated image

[estsauver]

What happened?

If a dspy.Image is specified as a Signature's output, it does not generate an image but will either pull a stock image or hallucinate a url.

Currently, models such as Openai 4.1/Google's Gemini support generating images natively in their responses api. It'd be great to support that directly. If that's not possible or is far away, then there should probably either be a warning if an image is specified or it should be restricted from being an output image.

Steps to reproduce

import dspy
lm = dspy.LM(model="openai/gpt-4.1")
dspy.configure(lm=lm)

class Image(dspy.Signature):
    image_description: str = dspy.InputField()
    image: dspy.Image = dspy.OutputField()


if __name__ == "__main__":
    try:         
        image = dspy.Predict(Image).__call__(image_description="A picture of a cat")
        print(image)
    except Exception as e:
        print(e)
        print(lm.inspect_history())
        raise e

➜  codewalker git:(main) ✗ uv run imagegen.py
Prediction(
    image=Image(url='https://images.unsplash.com/photo-1518717758536-85ae29035b6d?auto=format&fit=crop&w=600&q=80')
)

DSPy version

2.6.23