We would recommend that you always use a dry adhesive for sticking your photos into a scrapbook, unless you have a particularly large print, in which case you may like to opt for a spray as they cover a larger area more easily. Dry adhesive comes in the form of tapes, dots and photo mount corners.
If you do use a spray, we recommend acid-free sprays, as we simply don’t trust other wet adhesives not to ruin snaps by creating wrinkles or drying in a way that makes the glue brittle.