iPhone shows 1.3GB of photos but I don't have any
I'm pretty sure I have your answer!  I just had the same problem myself.

It seems that the Photos app has a "nice feature" called "Recently Deleted" that CONTINUES TO KEEP deleted photos on your device for a certain period of time.  SO ... Just click on your photos app, then click on its RECENTLY DELETED folder, then empty its contents.

Hope that helps!