Former picture framer here, u/QuOtak is spot on but I’d also add- if your picture gets any sunlight, UV glass will protect it from fading and spotting. It’s pretty expensive to frame correctly but it’s worth it for your important photos/art. Nothing would bother me more than seeing a family photo framed with regular glass and cardboard backing (not acid free). That family photo isn’t going to last. There are amazing scan/restoration services for situations like this, but again- good preservation work isn’t cheap and cheap preservation work isn’t good.