Why is there a blue dot at the left top on my screen

[iMore Question]

I just noticed a blue dot popped up on the left top corner of my phone, and when I click it a black box pops up but then goes away, and it's there everywhere like I could be on an app and it's still there or I could be on my home screen and it's still there. Help?

 

[phreddyl]

If you could take a screenshot that would help. Have you tried rebooting your phone? Are you near an Apple Store