robots.txt help

How do I disallow Google Image search from indexing my images but otherwise allow Google and others to index all of my pages text-wise? What I wrote in my current robots.txt file must be wrong because many months later and I'm still getting tons of referral traffic from Google Images. I find this disturbing because I don't want creeps finding photos of my children when searching for unrelated stuff - which keeps happening.

Bonus points if you can tell me how to accomplish the two tasks above (disallow Google images while allowing all other traffic) and also disallow one single directory too, which we'll call /thisfolder/

Thanks a ton for the help.