i was thinking very briefly about it, my answers were for creating one that looked good in Photoshop. Simply put high pass will reveal where contrast is. starting with the original pic, turn it into a 72 dpi image , that is about 600 pixels wide. do this useing the menu, image size. click ok, when done. save as. 72dpi.psd. ok. duplicate the background layer once. apply the filter 'highpass. to the background layer. use 3 pixel radius?. fade the layer abouve it by changing the layers opacity try 50%. go to the layers menu, i think and flatten image. paint the image area that you don't want black. i'd be interested to see how it resolves (forgive my dixlexic spelling)