The plug-in, called Contact Album, stores all the icons that your contacts use over time and comes with a viewer for the icons.
After installation of the plug-in, the album will slowly fill with icons as your contacts change them. You can open the album viewer with the Contact Album entry in Adium’s Window menu and with the View Album entry in the context menu for contacts.
Currently the plug-in comes with English, Dutch, Finnish, French, German, Portuguese, and Swedish localizations. Further translations are welcome.
Install the plug-in: Contact Album
Please note that the plug-in requires Adium 1.3 or newer and Mac OS X 10.5 Leopard.
Get the source code. It’s available under the GNU General Public License, version 2.