Suggestion: Document pitfall for Android usage

[jb-gcx]

Android OS automatically redacts (replaces with 0) Geotags from Exif Data, unless the App has requested the ACCESS_MEDIA_LOCATION permission. This behavior is documented here.

This resulted in the Hashes not matching on Android, while the same image validated successfully on a Mac. It took a lot of debugging to find, because the last thing we expected was Android silently modifying the files content upon reading.

I would like to suggest adding this piece of information to an FAQ/Pitfalls section to help out others who might want to use this SDK on Android.

[scouten-adobe]

@redaranj @n8fr8 would you please check to see if this is still an issue? If it needs attention in the core Rust SDK, please let us know.

[n8fr8]

If there is an issue, it is not a core Rust one, and more developer guidance / pitalls as the reporter suggests.

I think the specific issue is with a claim validator app that does not have location permission, opening a photo generated by a third-party app in a way that the EXIF is modified on the fly as the photo is retrieved for use by the app. I agree this would break the C2PA signature validation, but I will try to recreate it myself.

Would this also happen with a browser upload as well? We haven't encountered that in our work on https://check.proofmode.org via Chrome on Android, but maybe that is because it has the location permission.

[n8fr8]

Also another aspect to this is if you are accessing photos via the contentresolver and a Content URI stream or via the filepath. There are still ways to get to the root filepath that may also get around this dynamic EXIF privacy filtering.