Ideally, this preview image should directly whet the appetite for your map. So it is best to use the most beautiful section of the map - or a very characteristic section - for the picture.
Text on the preview image is of course allowed, but we recommend that you keep it to the name of the map and perhaps the author, so that international players are not disadvantaged.
The picture has to be 360 x 250 (W x H) pixels and may have the format *.bmp.
Highlight your map with the thumbnail. 
