How can Skype track downloaded file on the file system? Using Skype 7.37 on OS X El Capitan, observing this highly unusual behaviour:


I receive a photo in a Skype chat.
I click "Reveal in Finder", Skype places the photo in my Downloads folder as it is configured to do.
I move the file to eg. Dropbox.
I click "Reveal in Finder" again - Skype correctly opens the Dropbox folder!
I move the file again to eg. Desktop and rename it by appending "test" or such.
I click "Reveal in Finder" again - Skype correctly opens Desktop!!!


In steps 4 and 6 I was totally expecting Skype to download the photo again and store it into Downloads.

Can anyone else replicate this behaviour? How is Skype able to do this?
I don't use Skype but I suspect the fact it came from Skype is stored in one of two places. To find out, copy a Skype download to your Home directory and start Terminal. If your file is called, say, photo.jpg, you would run:

mdls photo.jpg


to list the metadata and something in there will refer to Skype or its bundle identifier.

Alternatively, run:

xattr -l photo.jpg


and see if Skype is listed in its WhereFrom attribute.