Set featured image from external url

Hello, i ve tried to find a solution reading 1000+ posts but still not get the goal… pls somebody help me.

I would like the featured images for all posts in my homepage to be external (not from my media lib) but from my imageshack account (for example), so i can save some bandwith (i have only 10gb with my host)

i saw a lot of websites doing it.. for example:

http://www.streamingreload.com

The timthumb will work in this way when i try to copy img url:
http://www.website.com/wp-content/themes/thumb.php?src=http://imageshack.us/image.jpg…

there is a plug in for doing it or some easy code to put (i am not a php expert).

i ll appreciate any help, thank you all.