Where does IE9 look for the large favicons?

Question

IE9 has the concept of pinning a particular website to the Windows7 task bar. For certain sites (such as Facebook), it will then display an extra large favicon in the task bar,

Answer 1

It's a bit late, but I found the answer above to be somewhat incomplete.

ico files can contain multiple images at the same time. So you can for example put a 16x16, a 24x24, and a 32x32 image inside a single ico file. This way IE can use the image with the most appropriate size. So it will use 16x16 inside the addressbar, the 32x32 for the taskbar (pin), and the 24x24 for next to the back button. If you want them to look better on hi-dpi screens you could use 64x64 instead of 32x32, and 48x48 in stead of 24x24.

You could even use different kinds of images instead of the same image in differently scales; so e.g. just the logo on the 16x16 and 24x24, but the logo and brandname on the 32x32.

One tool for creating such icons is the commandline application png2ico, or icoFx if you like a GUI.