That depends on how good you are with the image software
2 pictures are required for each unit; one for the selection menu and one for the ingame sprite:
Obviously I'm currently just copying the Vassal sprites (albeit changing the colour), but photos of units would be equally acceptable.
The actual size of the pictures doesn't matter, since they're scaled to the correct size in the engine. Obviously bigger pictures therefore mean higher resolution images. Make sure the pictures are square and ideally a power of 2 in size (128x128, 256x256, 512x512 etc). JPG or TGA are both acceptable, format-wise.
The circle on the unit picture is just to indicate the limits of the circular base; it doesn't need to be on the actual sprites (in fact the grey area should be whatever colour you want the side of the base to be. Ditto for the black, that should be whatever colour you want the top of the base around the models to be.
I'm pretty much finished with the marine menu graphics, and should get the marine unit graphics done tomorrow.
