is there a way to make a privite picture folder

Nope, there is no way.

If you lend your friends out to others and they go through your pictures but respect your text messages, then one thing you can do is save a picture in a text message (technically, picture message), then remove the original picture from the phone.  That way, you can still see that pic on your phone since it'd be in the sent box of whomever you texted it to, such as your e-mail address, and will no longer be in your micro SD card's "My pix" folder.