Have you ever done this? You pull your phone out to take a pic, but instead you snap off four or five. You tell yourself that you will pick the best one later, and delete the others, but you never do. Over time your photo library becomes cluttered with extraneous photos.
Cull gives you a simple and intuitive "Tinder" style swiping interface to remove these unwanted, low quality, pics cluttering up your photo library. Swipe right to move thru your photos. Swipe down to move a photo into the trash can. Tap the trash can to delete.