sorry to resurrect a slightly old thread for my first post but i was googling for a solution to this issue and was directed here.
i work in a photo processing environment and customers often come in for quick image prints off their mobile devices. recently i've been experiencing the OP's issue with iPhones. we have for the last 4 years of operation always been able to print camera roll images through our self serve printing kiosks via USB - as long as the camera roll was open before connecting the USB lead - however in the last 4-5 months there's been an increase in customer devices not being recognised after the 'Trust this computer' dialogue. this must be due to some change with iOS7 as my old 4S, which is still on iOS6.1.5, connects and allows printing without conflict.
i'd welcome a solution, our kiosks are Windows based and the Mac option suggested hasn't worked. thanks