irregular form gui shape

I've been able to make circles and triangular shaped guis using regions, but is there a way to have the gui in the shape of an image? For instance, what if I have an image of a bicycle and would like to make this the gui... I just want the bicycle to show up or what ever image is used. This is not possible with regions because it won't work by just clipping regions... How can I do this? I've seen guis where the gui is in the form of a person... So it's possible but I just don't see how? Any help...