If you are feeling lazy and don’t want to look up exactly how to instantiate a webcam and use it to take a snapshot of the user… just download this and use like so. It also flips the image so the user is not completely disoriented.
The default camera size is 600 x 400, you can pass two optional params to the constructor to specify different dimensions.
btnToPress.addEventListener(MouseEvent.CLICK, onPictureSnap, false, 0, true);
var userpic:Bitmap=new Bitmap(webcam.snap());