you just use ordinary ‘cylindrical projection’ (Miller projection if you will .. http://en.wikipedia.org/wiki/Miller_cylindrical_projection ) So, do you want to map a SQUARE image on to a SPHERE. Or do you want to map a ROUND image on to a sphere, or do you want to map a TRIANGLE image on to a sphere – or conceivably some other flat shape, you want to map on to the sphere. Of course, it’s apparent you very likely mean a ‘square or rectangle’ since that’s what PNGs almost, always, are :) Finally it’s worth noting that ….. you can map from a flat PNG on to a mesh surface …. any way you like! You can ‘bend and distort’ if you will, as you happen to want. Indeed, that’s exactly why assembled textures / maps for dinosaurs or whatever (made by something like Unfold3D) look really weird and bent (if you map a head or something any possible ‘choice’ will look weird and bent). Attachments: Up to 2 attachments (including images) can be used with a maximum of 524.3 kB each and 1.0 MB total. Source.