fun fact for the day: images uploaded to need to have less than 12.5 million pixels, or the thumbnails will be broken.
This means that the image size should be less than 3535 x 3535 (Obviously if one side is shorter, the other can be longer)
This is annoying, since the full size of the SR2 map is 5808 x 5642, so accuracy will have to be sacrificed.
edit: Specifically, map images will have to be reduced to at least 75%. Fortunately, it's a simple matter to scale the placement of the markers, so it is only resolution that is sacrificed, and accuracy will still be within 1 pixel :)