I get what you're saying, but I don't think I entirely agree. If we live in a world where you can't tell if a picture is real or fiction, then it becomes necessary and reasonable to think of all pictures as fiction.
Granted, if your grandparents are showing you their vacation pictures from their world travels that never happened, this is a different scenario that is weird and can could happen. It’s a balance of trusting nothing you see while making a few exceptions for your family and whatnot
Being 100% convincing doesn't make it true. Not being able to tell what's true from what's fake is a self-evident problem. It means you're at risk of forming an invalid view of the world. The only safe approach would be to never believe anything, at which point we've even lost recent history. Madness lies that way.