How can I get rid of a blue frame moving over my screen all the time?

[Gabi]

I've got a new used iPhone 4s. Suddenly a blue frame occurred on my screen and is jumping around and changes its size. The other functions can still be used normally. Switching off and on the phone did not help. How can I get rid of that blue frame?

 

[Rob Phillips]

Welcome to iMore! I might recommend restoring through iTunes using recovery mode. Instructions here: https://support.apple.com/en-us/HT201263
This will force iTunes to reinstall iOS. Before restoring from a back up, set it up as a new device and see if the problem persists. If the problem is still there it could be a hardware issue and I would contact whomever sold you that 4s.