You want to protect your photo and ensure that it does not slide down in the frame over time. The best way to do this is to buy a frame that is one size bigger than the size of the photo.
For an 8”x10” photo, you want to buy an 11”x14” frame that comes with a mat around the photo. The mat will keep the photo from actually touching the glass and sticking to the glass over time.
Now that you have the phot behind the mat, gravity takes over and the photo slides out of place. There is a simple solution for this as well.