The "If Found Lock Screen" app is meant to be used to add some text over your lock screen picture, e.g., "If found email xyz @ gmail.com"
I used it for that purpose and found that when it finished it saved a copy of the picture with text to the Camera Roll. I'm pretty sure it allows you to start with your current lock screen picture but not sure if you can trick it into saving the picture without any text. If not, you may be able to add a single character of text near the top or bottom and edit it out later. Worst case you'd be out 99¢. Here is a link to the app: https://itunes.apple.com/us/app/if-found-lock-screen/id398340788?mt=8
This is why we need better photo management, people lose valueable photos all the time.
Imagine hundreds of millions of children whose childhood is being stored on devices people don't know how to properly backup. By the time these kids are adults, most of the valueable stuff will be gone.