How to save stock ROM before flashing with new?

[DanLSmith]

I'd like to copy/save the folder that contains the stock image that 'reset to factory' in settings uses. This way, I can install a custom ROM and if I don't like it, then I could simply copy this folder back to it's original location, and then (wouldn't?) 'reset to factory' see it and use it and make the tablet like it was originally? Where is this folder or file located? I have a Hyundai X Play RK3188 that is rooted, with ver 4.2.2 on it. Since it's the android OS that does the restore to factory settings, shouldn't this backup image be in the same location for all android tablets? Thanks in advance for your help.