Okay, if you have a recent version of Microsoft Word, or Open Office, on your computer, this is worth trying (though all of you graphic geeks are going to laugh at it):
Copy the picture to your clipboard. Open Word and paste the picture in. Then, right click on the picture and choose Format Picture from the menu that opens up.
Then you want to reset the color, contrast, and brightness options till you get something more like a line drawing. Start by setting the color to grayscale or black and white, then start pushing the contrast slider up and down.
Not as good as a graphics program, but a cheap workaround!