How do you know if photo was deleted from image gallery?

Doing some research, I was wondering how to handle the creation/deletion of photos from the photo gallery. I was hoping to be able to create an app that allow users to take photos or select them from the gallery. However, how would I be able to know if the photo was removed? Should the photo be saved within a file structure inside the app, added to the image gallery, and only way its removed is from within the app but still maintaining the photo gallery since its out of scope?