Hey there! Let's break down why your album-based image uploads are failing while the bundled flag.png works perfectly—this is a super common issue in iOS development, so let's walk through the most likely causes:

• Missing or Denied Photo Library Permissions
  When pulling images from the user's photo album, iOS requires explicit permission to access those assets. If your app hasn't requested the Photo Library permission (or the user denied it), you might end up with an invalid URL or be blocked from reading the file's content entirely. Bundled resources are part of your app's sandbox, so they don't need extra permissions to access.
  Double-check that you've added NSPhotoLibraryUsageDescription (and NSPhotoLibraryAddUsageDescription if you're writing to the library) to your Info.plist with a clear explanation for why you need access, and confirm the user has granted the permission in Settings.

• Incorrect Handling of Photo Library URLs
  The URL returned by the photo library is usually a ph:// scheme URL (pointing to a PHAsset), not a direct file system path. If your upload code is expecting a local file URL (like the one from Bundle.main.url(...)), it won't be able to read the image data correctly from the ph:// URL.
  Instead of passing the album URL directly, use the Photos framework to fetch the actual image data. For example:

  PHImageManager.default().requestImageData(for: yourPHAsset, options: nil) { data, _, _, _ in
      guard let imageData = data else { /* handle error */ return }
      // Use imageData for upload
  }
  

• Sandbox Restrictions on External Files
  iOS apps run in a sandbox that limits access to files outside their own container. Photos from the album are stored in a separate system-managed location, so trying to access them via a direct file path will fail. Bundled images live inside your app's sandbox, so you can read them without restrictions.
  Always use Apple's official Photos APIs to retrieve image data instead of attempting to bypass the sandbox—this is the only supported way to access user photos.

• Unsupported Image Formats
  Your bundled flag.png is a standard PNG file, but photos from the album might be in HEIC format (the default for newer iOS devices). If your upload server or code doesn't handle HEIC files properly, the upload will fail.
  When fetching images from the album, specify a target format (like JPEG or PNG) in your PHImageRequestOptions to convert the asset to a supported format before uploading.

内容的提问来源于stack exchange，提问作者aaisataev