Recover photos

I updated my os x to os x mavericks, however, I did not think to back up my photos before doing so, by the time i thought about it the update had already been completed. My old photos are now located under system preferences>Screensaver/Desktop, how do i go about getting my photos back to the iphoto file that the computer already came with? Other ways to transferring photos are open too. I wish to recover my old photos without spending a lot of $$. Please help. Thank you.