Need more details about what happened, did you delete the files accidentally? You typed in the post in the title field which cuts off after so many characters.
If they were not backed up to the cloud (say with Google Photos) or a computer, there is pretty much no way to get them back. You can try connecting the phone to a computer and run a file recovery program against it like Recuva, there are also file recovery apps but they all need the phone to be rooted, so you will need to do that first.
For next time I suggest you install Google Photos and allow it to sync your pictures to their storage for backup and easy sharing, and backing up the phone data to a computer is also a good idea. Don't just keep files or info in your phone that can get lost/stolen/damaged/dropped/etc.. easily.