Can’t get rid of wallpaper

I clicked on http://antwrp.gsfc.nasa.gov/apod/ap050613.html from one of Techrepublic’s email links (great space images) and “meant” to save the image as a file on my desktop … but my fingers worked faster than my brain and it saved the image OVER my existing wallpaper. I have not been able to find the file to delete it. I searched the entire C: drive for *.bmp and *.jpg files added today.
The image only appears on my profile and superimposes itself over any display background I choose. How do I get rid of it?