The answer to the camera question is easy to me.....because not everyone can afford the proper camera setup to take high quality pictures.
I have done both with banknotes. Scanned and taken pictures. The scanner is just much easier. It's easier to place the banknote so it is level, so when you view it, it isn't tilted any.
With a camera you need to make sure you have a piece of paper taped down for a background and to get the camera set so it takes level pictures. Most people don't want the hassle of setting the camera up this way. When tyhe edge of the scanner glass will do it for you.