Tim --

No magic insight into the Nav system. Standard computer "photos" are 4:3 and for that size screen 640x480 is a probable size. You're probably going to have to experiment with a couple of sizes but 640x480 is a good starting point. It may be lower.

My on top of the dashboard GPS unit has a 640x480 display and can display photos too. This has a 6" screen.

-- Chuk