Perfect Image Cutting?

Hey there, i've seen some pretty amazing signatures, with say an object that has been pulled out of a picture, but im not quite sure how they do it, i know that you can do the Magnetic Lasso Tool, but that sort of fails and it always looks scruffy with a crapp cut.

Please If You Know Any Ways Of Doing This Let Me Know
Thanks
Pukey

 

well if your render and its background are two totally differnt colors then use magic eraser. its fast and you wont have to worry about it take some pieces off