Welcome to Android Central! If you're talking about Google Photos, then keep in mind it's essentially all virtual. With Google Photos, you upload your photos to the Google Photos cloud. If you create an album, it's a virtual album where you can assign any of your photos to be part of the album. One photo can be in multiple albums -- you're not making multiple copies of the photo. Removing a photos from a Google Photos album doesn't get rid of the photo completely -- you can still find it in your main Google Photos stream. If you have thousands of photos, it can be a little hard sometimes, but that's where the search function can be very powerful. Let's say the photo you're looking for was of a boat -- just type "boat" into the Google Photos search bar, and you'll see many (if not all) of the photos in your entire library where Google's AI was able to identify a boat.