(Because “The Winning of Illusion” just didn’t sound as good.)
The Winners of the 2009 Best Visual Illusion of the Year Contest have been announced! There’s a ball that drops straight down, but if you look to the side while it drops it appears to fall at a different angle, a dove that appears to change color depending on the background, a pair of facesthat are identical except for the coloring (the one with more contrast between the face and eyes/mouth appears female, while the one with less contrast appears male), and more.
As a bonus, Arthur Shapiro, one of the creators of the dropping ball, has several other illusions up on his blog. These can be posted for non-profit educational use, but I couldn’t get the html code to work. Bummer.
Since a post on illusions would not be complete without a couple illusions, here are a few. This first one is called Sander’s Parallelogram or the Sander Illusion (after creator Matthew Luckiesh author Friedrich Sander), and the two blue diagonals are the same length. Seriously.
And finally, here’s a grid illusion. There are white dots in the middle, but black spots seem to appear:
And finally, here’s one in which the bar in the middle is the same shade of gray throughout, but looks like it’s changing color (courtesy of Dodek, published under GNU-FDL).
(Contest Winners found via New Scientist.)
This is the Impossible Triangle, also known as the tribar or as the Penrose Triangle. It was invented by 
360 
