Carleton has developed an extension for ContentDM which allows users to download the full sized version of any images they add to their favorites. This code works with ContentDM v4 and above, though it has only been tested on a Linux/Apache based server. It requires Perl and a few extra modules all outlined in the documentation.
Download the "Download Favorites" ContentDM extension (.zip)
Please feel free to contact Matt Bockol with any questions