How to enforce google not to index some folders?

[kalexis]

Hi, i have some amount of "images" folders in some places on my site, definitely they has just images inside. I can see that google indexes them. Does it can hurm the site by some way?
If so, how can i enforce google not to index them?

[Anothers]

robots.txt tutorial (http://www.searchengineworld.com/robots/robots_tutorial.htm)

[Alphawolf]

and...

http://www.google.com/remove.html#images

[kalexis]

thanks guys