Shy Ghost

It's been a while since I had this idea of an "interactive image". I decided that was the time to make it. I can't say if that's way too easy to find.

Here is the original image:
http://goo.gl/60kr9

People are supposed to find a way to discover the invisible ghost ^_^ from the image.
I think it works fine because the internet default background color is white (as the ghost). Ghost are usually scarred from the light, so they appear when it's darker.
Anyway, try it and let me know what you think.