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

Please read the following article
How to enable IE9 pinning and Jumplists

Create a High Definition Favicon

Standard favicon files are usually 32x32 or 16x16 pixels in size. These look great in the browser but when you pin it to the taskbar it can be a little small and pixilated.

To give the best pinning experience you should use a 64x64 favicon. I used http://www.favicon.co.uk/ to create a 64 x 64 icon file and then uploaded it to my site.

You then need to make sure you are using the new favicon by checking the tag is pointing at the new 64x64 fav.ico file.

Basically you now can create a larger favicon file, and IE9 will use it in the task bar. However, if you have a standard size favicon, IE9 will still use it.

An added benefit is that you can implement an awesome JumpList to enhance the visitors browsing experience.

Further reading: http://www.hanselman.com/blog/IE9SiteSpecificBrowsersAndAddingYourOwnJumpListItemsToPinnedTabs.aspx

Answer 2

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.