How do you free form copy on Mircrosoft Paint without the box around the selection?

[the red pigeon]

So, I'm trying to post someones head into another picture. But it keeps looking retarded because It has a white box around it. The best thing I know how to do is fill in the background with the closest color to the back of the pic i can get.

I would like to know how to get rid of this box, too make my life alot easier.

I'm on windows vista.