CSS3 transitions are used to “add some drama” to an image, in a way that’s reminiscent of the effects used in some slideshow applications.
I “stole” the image from this page, and I claim no ownership of it, I only find it useful for explaining the effect (Miku is also cute, of course :D ). If there are any problems with that, I’ll pull the image.
The image is included with a data URI.