Microsoft Foundry Agent via Responses API rejects local image input as Base64 data URL / byte array

Hello everyone,

we are seeing an issue with the new Microsoft Foundry Agents via the Responses API when sending a local image as part of the user message.

What works

• text-only input
• image by public URL

What fails

• local PNG passed as Base64 data URL
• local PNG passed as raw byte array through SDK methods

Example failing image part:

{ "type": "input_image", "image_url": "data:image/png;base64,...", "detail": "auto" }

Returned error:

{ "code": "invalid_payload", "message": "The provided data does not match the expected schema", "param": "/", "type": "invalid_request_error", "details": [] }

We reproduced this in:

• C#
• Python
• raw REST

So this does not appear to be limited to one SDK.

Also important: the same pattern is used in the sample repo for the Foundry Agent Web App, and this scenario worked for us about one week ago:
https://github.com/microsoft-foundry/foundry-agent-webapp

Could you confirm whether local image input is currently supported for Foundry Agents through the Responses API, or whether this is a regression?

Best regards