thats so weird that i cant get it to work on mine
Doesn't it only show full screen photo while the phone is ringing? And then once you answer it goes blurred background. I think that's how it's supposed to work?
Do you use gmail for contacts or icloud?
I believe that if you're using gmail, you need to add the contact picture from your phone in order to get full screen pics. If you've added the photo through the gmail website on your computer, you won't get full screen pics when someone calls.
I'm pretty sure that's how it used to/still does works when using gmail for contacts.
It might be the same if using iCloud also. Test it out. Add a contact photo from your phone and see if it comes up full screen.
Here is a trick - if you see the small photo in the corner, but you want the photo to be full screen when you get the call, just go into Contacts and edit the picture. You just need to open the picture in edit mode and save it. Once you do that, the picture will be full screen when the call comes in.
This is how it works in iOS6 and earlier.