You can use a video camera hooked to a digitizing board in your computer to capture images. The digitizing board, often called a frame-grabber, converts the analog signal from the camera to a digital format that can be read and enhanced by software the same as a scanned image.
The biggest difference between a scanner and a digitizer is that a scanner can only capture an image from a two-dimensional source, such as a photograph or slide, while a digitizer can capture any video image. A digitizing board usually captures two-dimensional images faster than a scanner, but it doesn't necessarily provide the best quality for the money. So, unless you're willing to get the best equipment, you might be better off buying a scanner to capture two-dimensional images.