What Criteria Or Method Is Used To Cycle The Images In Desktop Slideshow

I'm using Windows 7 Ultimate 64 bit.I use the desktop slideshow feature, directed to a folder in my pictures folder that I named desktop slideshow, I have about 1000 images in there, it's set to change image once every 30 seconds.Here is the problem, I tend to see the same 20 images or so go by over and over, and only once or twice in each loop does a new image show up, eventually I see a great number, but it tends to favor those same 20 or so images predominantly.They don't have similar names, they are widely differing in size, dimensions, and every other aspect. But for some reason the slideshow tends to pick them to go by more than anything else. I removed the images, and it chooses another 20 or 30 seemingly at random to give priority over the rest, only slipping in a random one between those repeated choices once or twice in each loop again.

So here is my question, does anyone know what criteria or method is used to cycle the images in the desktop slideshow? The whole reason I started using it was because I like the idea of seeing any one of a thousand or more pictures on my screen when I close a window, and it's kind of nice to have something I'm working on in my main screen while random art goes by on my second monitor, but with the same images repeated, it sort of loses the appeal.So far my only option has been to remove the over used images after a while and cycle in some of the old ones I removed before. But that's not really all that satisfying a solution.I searched around google, talked to some friends, and generally applied my brain to the issue for a few months without any breakthrough, and decided to seek some info from this forum since it seems to be fairly chocked full of people who have considerable knowledge of the concerned operating system, big surprise considering that is the point of the forum eh?