I hadn't backed up for a while so I feel a loss here. About 400 photos just gone from my photos on my samsung. I checked in folders and not there. I never deleted them. All photos from about February 2017 onwards and random ones prior. Some are of my Dad's 90th and my nephews wedding. Drats. For some reason my phone hasnt backed up since July 2016, says it failed and when i go to back up it says failed as an unknown error has occurred. My memory was pretty full too before these photos went missing. Google says i need to download an app to recover. Is that the solution? Thanks in advance.