I have a fair number of image folders holding pictures for my eyes only.
sometime my kids use my iPad playing games, and it is also used at work and sometimes end up in other hands than mine.

Is there any way i can lock some of the photo folders in photos??

Use Stash app. Works great and is password protected.

I use GoodReader app; created password protected folder and moved pics to it using iTunes. Can also try dropbox app but pics are not stored local but in the cloud. Both good reader and dropbox have built in gallery viewer instead of using native iPad photo viewing which leaves record.