http://serverfault.com/questions/127795/tar-a-directory-and-only-include-certain-file-types

find tilesets -type f \( -name \*\.png -o -name \*\.GIF -o -name \*\.gif -o -name \*\.PNG -o -name \*\.BMP -o -name \*\.bmp \) -print0 | xargs -t0 tar -cvzf tilesets_new.tgz