Most likely out of storage space. Try clearing up some space by deleting some old photos or uninstall apps you don't use. If you have sd card just back it up to your PC and wipe it clean before putting it back in the phone
Try backing up your pics to a Cloud storage like Dropbox, Google Drive or Microsoft.
Check your storage space
If you do not have an SD Card for extra storage and have too many apps installed... it is possible you might have ran out of Internal Storage. Look at Storage in Settings Before taking your phone in to be diagnosed try and uninstall anything you do not absolutely need.
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