Just install es file explorer. In that go to phone memory - hold the whatsapp folder to select the folder -now in options select hide ( with the lock symbol, it's in top ) . If you want the same password protected, in ES go to settings and password settings - hide list password. Voila you can't see the whatsapp in album. Still you can access whatsapp and see pictures. If you want to lock it any app locker would do fine. I prefer smart app locker.
