There is product called UnDo. It is non toxic and won't harm photographs stuck to glass frames as it removes them. It's now sold in a small bottle for the public instead of by the drum or gallon. Walmart has it but it's hard to find, could be any dept. It removes stickers, bumper stickers, gum, adhesives, anything stuck. It evaporates and leaves no residue. I keep a bottles in the kitchen, my sewing room, and in the laundry room. Don't buy the one labeled can be sold in CA. I tossed that one, it just wasn't as good.
https://www.un-du.com/Products.html