This story happened to me just a few weeks ago. I had been visiting several cemeteries, snapping photos and trying to capture EVP's (electronic voice phenomena). I jumped in the shower that night as usual, and was coming out of the shower when I looked to the mirror. Sometimes, mirrors fog up when the door in the bathroom is closed, but, it fogs up all over the mirror. Today, however, there was only one spot fogged up. Lengthwise, I am guessing that the skull I saw there was a little less than a foot long.
I didn't have my camera handy to get a shot of it! The next day, the same thing happened, but the skull image began to dissipate, as if the water from it was streaking down the window.
Since then, I haven't seen it reappear, but, I am still watching for it. Any explanation I can offer to myself here is that somehow something tagged along home with me from one of the cemeteries for those 2 days.