Photography relies on physical law - the image is made by certain photochemical and optical procedures. So to be photography, it needs to be done with those techniques. Once you use computers to manipulate the picture, it ceases to be photography. That's fine, and I like a lot of digital art. On the other hand, if the digital artist passes off their work as photography, they're cheating.
This isn't to say that digital tools such as digital cameras, scanners, computer controlled printers, smile detectors and the like cannot be used. It's how those tools are used that makes the difference.