1. Problem Summary

When trying to upload an image saved through the X (formerly Twitter) app directly to GPT via the iPhone Photos app on an iOS (iPhone 13, iOS 17.x) environment, it was discovered that the MIME-type of the image is not recognized correctly, leading to a null response during the Action API request, resulting in a 400 error. Despite the image format being JPEG, OpenAI's file service fails to infer the MIME type correctly.

2. Conditions for Occurrence

  • Device Used: iPhone 13 (iOS 17.x)
  • Upload Method: Direct upload from the Photos app to GPT
  • Image Generation Path: Saved via the download button in the X app
  • File Format: JPEG (based on EXIF information and compression method)
  • File Extension Notation: .jpeg or .JPEG (Photos app) → .jpg (as confirmed when synced with Nextcloud on Ubuntu)
  • Photos App Behavior: Automatically categorizes images saved from the X app into albums

3. Summary of Experimental Results

Experimental Condition Source Extension MIME Inference Value Result
Upload X image from the Photos app X app download .jpeg null ❌ Failed
Copied to Files app/Nextcloud and then uploaded Copy of X image .jpg image/jpeg ✅ Success
Upload same image on Ubuntu Folder synced with Nextcloud .jpg image/jpeg ✅ Success

4. Analysis and Estimated Causes

4.1 Possibility of Metadata Interference from X App

  • iOS-specific meta tags like com.apple.metadata:kMDItemWhereFroms may interfere with MIME-type inference

4.2 Discrepancy Between File Extension and Internal Format

  • While marked as .jpeg on iOS, it is treated as .jpg on platforms like Ubuntu, leading to differences in inference methods

4.3 Ignoring the MIME-type Specified by GPT

  • Even if GPT specifies image/jpeg, OpenAI's file service ignores it and processes it as null

5. Suggestions and Approaches

5.1 User-side Response

  • Do not upload images saved from the X app directly via the Photos app
  • It is recommended to transfer the image file via the Files app or PC/Mac before uploading

5.2 Request for Improvements to OpenAI and Action SDK

  1. Improve MIME-type inference for .jpeg extensions
  2. Enhance the SDK to ensure the MIME-type specified by GPT is not ignored
  3. Consider Fallback processing based on Content-Sniffing without reliance on metadata

6. Available Reference Materials

The following materials can be provided upon request: - Screenshots comparing metadata in iOS Photos app and Ubuntu environment - Media property information extracted from Ubuntu - Actual request logs where the MIME-type specified by GPT was ignored