I have seen on some other sites that the webcam on your computer will not be sufficient for this kind of work, and that totally makes sense to me. I had purchased a Microsoft Lifecam and it worked twice and now it does nothing at all. What kind of webcam do you use?
I recommend you go to special stores that sell computer related stuff and buy whatever they recommend you. Usually the people working there know their merchandise so asking them for advice on the products they have is no going to be a problem.
Any high-end webcam made by a reputable manufacturer will do, but if you don’t know where to start, read some reviews on CNET or Consumer Reports. Both websites have reviewed webcams in the past and list the pros and cons, along with the price, of every cam they’ve reviewed.