wow nobody replied to this?
Theres an easy lazy way and theres a more time consuming way. Time consuming will look better..
Easy way -- Go to photoshop click select the magic wand tool, select the layer with the render and click on the "black" part of the sig. Now right click on the black part and select feather, set it to 1 pixel click okay. Now hit delete a couple times, or as many times as it takes to get rid of the spots... You can set the feather to higher pixels but that will delete more of the picture in the process...
Hard way -- take the eraser.. zoom in... erase!