Why not just name the images after the board keyword and use that to get the image source? Then the only thing needed would be a image tag in the template looking something like this:
code:
<img src="{$config['images']}/{$forum[$c][$f]['Keyword']}.gif" alt="{$forum[$c][$f]['Title']}" align="left">
And just put it in the ubbthreads.tmpl right before the line with the forum description:
code:
{$forum[$c][$f]['Description']}
Then just create the pictures, put them in the image directory and name them after the board keyword and with the correct image extension.
In this way there is no need to change the database, it's just a matter of changing the template.