The browser itself is actually doing the alignment. Looking in Firebug or the developer tools for Safari or Chrome show that the vertical-align CSS property is being inherited from the browser default style: baseline.
All of the images are inline on that page. By default, images are aligned to the "baseline" of a line of text, so that the bottom of images are aligned horizontally with the bottom of many lower case letters like "a" or "z".
Nothing special is being done at all. That's just how browsers render images naturally.