In this case, I don't think it requires much art skill. More of an artistic eye. If you think about the shape of the banner while bringing up a nice crack of dawn image from Minetest, then you can hit f12 and then crop the image and adjust the dimensions. I don't know what the banner options are, but if it is a changing banner, then take a lot of snapshots. Get on some of the creative servers and snapshot skylines.