@Grumpy_Mike would that work with a webcam, because the webcam is surely USB based and it therefore doesnt output analog video. Would be cool to use with a webcam or small analog camera though!
Otherwise Ntech if you want to interface to a USB Webcam its going to be quite hard because as was mentioned you need a USB host controller and nice processor. You might be better off getting a little single board computer or something that is more like a small PC and runs Linux