u need to create 1 logo with transparent background. size 24 x 24 . and save in bmp format.
after that u go to ur noscrubs iris foder/guildmark - delete 1 file name : mark.bmp
after that u rename the new logo that u just create with : mark - and put into guildmark folder
then u login ur char - Guild section - manage - emblem
ur new logo should be there....and voila......u will have new guild logo.....

After awhile suddenly it worked as i just changed the name from mark.bmp to just mark >.

if the picture aren't appearing, u just need replace it over one of the pics what u'll find there... Example:


i'd created one guild mark, going to save as bmp on the right folder, and, when i open this folder, i click to replace one old other...

i hope u can understand...