Sounds like something on the phone is removing things. It can happen with updates, but usually it is something else, bad app, virus, malware, etc. If they are files that were on the phone itself, then you can 'try' the following to see if they can be recovered. I would also suggest checking the phone for the things mentioned.
NOTE: If the images you were using came from an app, then it is completely possible the app itself removed them.
While there is no guaranty that you can get them back. Deleted does mean deleted. There are a few apps/programs out there that 'may' be able to help you recover the data.
A few of the programs you could try would be... DiskDigger, MobiSaver, Android-Recovery and Tenorshare. They are all data recovery...