This is a customization for a photographer with a more or less permanent relationship with his customer.
The users only have permission to view scaled versions of the image.
I introduced a new flag in the zipcart configuration that lets the ZipCart download module override permissions to access the fullsize version.
Each download gets logged to the database.
The admin (or any other user with proper permissions) can view the log.
It's a hierarchical view Year -> Month -> User -> Images (time, host)