Metadata for Google Photos "compressed" images

[nitin]

I was wondering if there is a metadata tag that Google Photos adds after it compresses images to 'high-quality' format. I did notice that some of these compressed images carry a tag in the "Program Name: Picasa". I am not sure if this is consistent with all compressed images... or if there is a better way to look for compressed 'high-quality' images in Google Photos

[StarGeek]

Make sure you read the ongoing comments between xiota and me on your StackExchange post. 

While I don't believe there's a way to definitely be sure a file has been recompressed, the best bet seems to be to check EXIF:ImageUniqueID.  I don't recall very many programs using that tag. 

So try:
exiftool -if "$EXIF:ImageUniqueID" -FilePath FileOrDir

That should give you a list of the most likely files that have been recompressed by Google Photos.

Edit:  Xiota's edited answer is probably the best one.