Keep images wide-screen if they were that way in the first place. Nobody wants a square screensaver. Also make the transition between slides changable (or a bit nicer) and prefably a 'random' mode for the slides.

Whenever I load up one of my photos and generate a screensaver, it will become a square (cutting of parts of my picture). Next to that it will start on the very right end of my screen (not centered).

The Transition between slides is kind of bad. It turns black and poof there is the next image. Perhaps fading in would have been a good idea as well. You need more options to make this program a better one.