Deleted photos keep coming back

[AC Question]

I have a Samsung S4 mini, and I'm having a problem with storage ('storage space running out' message), which I think is because I can't seem to delete any photos, they just keep coming back! At first I thought there were getting auto-restored from Dropbox, but I have disconnected my phone from Dropbox and it's still happening. I can't figure it out, please can someone help??