Here is background I made. It was made in GIMP, although I exported it to a .png and a Photoshop image. The dimensions are {1280w X 800h} here is to link to it.
preview:
.jpg:
https://www.dropbox.com/s/lklghuv1yed9ehp/mtb.jpg
.png:
https://www.dropbox.com/s/b1cp8j86apmchr3/mtb.png
.psd(Photoshop):
https://www.dropbox.com/s/yr3pzedfdn4i2xs/mtb.psd
.xcf(GIMP):
https://www.dropbox.com/s/ypyxfb71nv9dfd8/mtb.xcf
This only took me about 20 minutes. (about the length of a Minetest day.)
hope you like it. :)