Yesterday my wife was looking for some photos in the photo library, there were a couple of them that had a White exclamation mark in the bottom right hand corner, any question she comes to me.
To be honest, I was not aware and I had to look this up.
The exclamation point on an iPhone photo means that the photo is not original but just a copy of original. For that, select Download and Keep Originals option under Settings > Photos. When connected to Wifi, the iPhone will automatically sync up with iCloud and download the originals.
Hope this helps you out