BRPG's maximum map size for maps that will be used as battlemaps (i.e., those which require placing individual PC/NPC/monster tokens on) is 40 x 40 grid squares, or 40 x 46 hexes, so you would have to break down your master map scan into several smaller segments and load each one up as it's needed.
But if you're just planning on using the map as an Area Map (perhaps with a "You Are Here" marker on it), then the only restriction is that the map not measure more than 4000x4000 pixels.