Missing desktop image!?

[music_is]

I found a really great photo online, right clicked on it and selected "Use As Desktop Background" on my mac. Problem is that I never saved the image and clicked on another desktop background in the display preferences sometime later. I had no idea that my original background would automatically change! How do I get it back? I'm thinking it must have been saved somewhere on the computer for it to be used as a background image in the first place right? Please help, it was a really beautiful picture of the Golden Gate Bridge and I can't find it again! ;(