Fun Gameboy accessory project– The Game Boy Camera uses a cheap CMOS image sensor with a resolution of 128*123 and an analogue monochrome output. This page shows how to connect it to a standard non-bidirectional, non-ECP, non-EPP PC parallel port, with 5 bits per pixel, compared to the Game Boy’s 2 bits dithered. The circuit described here uses only the small PCB in the swivelling part of the camera, which contains the AR chip, lens assembly and pretty much nothing else. No Game Boy involved. Link.
Game Boy Camera Parallel Port Interface