How to find all photos on your Mac

Steve Thomas is trying to clean things up across two Macs:
I’m finding that there are photos EVERYWHERE on these two machines—Photos library, iPhoto library, Photo Booth library, multiple file folders on dozens of different levels and in countless locations.
He already owns PhotoSweeper, an app that handles de-duplication, but he’s frustrated at having to select all the folders that contain photos in order to perform a scan and then sort through the results.
How can I possibly