It's a small nautilus extension that's been forked quite a few times from what I can tell. The most current version of it resides in the WebUpd8 Ubuntu PPA.
It adds a ton of information that can be displayed in the Nautilus list view like artists and track titles for music files as well as dimensions and EXIF information for images among a ton of other things.
Nautilus doesn't seem to come with a way to sort image files by dimensions like Pantheon Files does so this is the next best thing for me and hopefully a lot of other users.
Here's the latest source tarball from the repo https://launchpad.net/~nilarimogard/+archive/ubuntu/webupd8/+files/nautilus-columns_0.3.3.orig.tar.gz