Nah, they probably thought they were new frames and havent been filled in yet. (I honestly dont know)

Fair enough lol

Good question...

Its very confuseing

Haha, but wouldn't they have remembered putting pictures there? And wouldn't they still see the backgrounds to the empty pictures? Also wouldn't Hermione have told them because its like a pretty cool wizarding thing???

No, because she did it so they were not in danger of Voldemort