They are just images with a reverss image transparency, one I think Henry posted a while go, another was just diagonal lines drawn in TC.
I've e-packed the file, with the images, though as its nearly a meg, I've put it here
instead of the forum.
If you wish to look, download and extract the zip, and in TC navigate to the TC file, don't move the file out of the folder or it may not be able to find the images.
It is not perfect but should provide an idea of how to use you own images.