Weird images in my screensaver??

I wasn't sure where to post this. I'm completely dumbfounded by this occurence.

My screensaver is set to show random images from my iPhoto library. For the last few days, who knows if it's been happening longer, I have occasionally seen this:

-First a photo fades up for a few seconds
-Then, the same photo fades in again, only it will have some random clip-art like image ontop of it, like a sunflower, or a red, white, and blue circle. Usually simple little images.

I checked my iPhoto library to see if they exist there. I see the original images, but I don't see the weird clip-art-layered-on-the-regular-images.

I wish I could get a screen grab of this becuae I realize how strange this sounds. My computer doesn't seem affected otherwise.

Is it a virus?

What gives?

Andrew