WordPress Questions (Modifying)

On the sidebar, if you look at http://www.ismithop.com/index.php you see there's the "Partners" and the "Recent" categories. I want the recent to draw up an image from a certain div class in articles from category "Portfolio". What's the best way to go about doing this? I want every article in "Portfolio" to be assigned a 50x50 .jpg that will be called into an array of 6 images on the sidebar.