Duplicate It!
Duplicate It! is an app that will allow you to save a "clon" of your photos in order to get them save before editing.
As you have a copy you can place it right after the original and check the differences once youre done with the modifications.
To make it simpler, Duplicate It!, installs an action extension that will allow you to duplicate photos directly from the Photos app, in the same way you send them to print!