Category Image in last 10 posts

This is my website:
http://frontpage.klifix.nl/

In the sidebar you see the last x posts with the date or time and the nr of comments listed with a truncatefunction.

I’d like to at an icon to each of these posts showing in which category it is posted in. Similar to this website:
http://games.fok.nl/

Currently I use this code:

<?php
$today = current_time('mysql', 1);

function truncate($string,$chars,$append = '...') {
if(strlen($string) > $chars) {
$string = substr($string, 0, $chars);
$trunc_at = strrpos($string, ' ');

if($trunc_at !== FALSE)
$string = substr($string, 0, $trunc_at);
$string = $string.$append;
}

return $string;
}

if ( $recentposts = $wpdb->get_results("SELECT ID, post_title,  post_date FROM dotenel_posts WHERE post_status = 'publish' AND post_date_gmt < '$today' ORDER BY post_date DESC LIMIT 25")):
?>

<?php
foreach ($recentposts as $post) {
  if ($post->post_title == '')
  $post->post_title = sprintf(__('Post #%s'), $post->ID);

$posttime = strtotime($post->post_date);
$mytime = date('<font color="red">H:i</font>', $posttime);
$mydate = date('<font color="red">d/m</font>', $posttime);
$currtime = time();
$today = date('d',$currtime);
$postday = date('d',$posttime);
if($postday==$today)
echo $mytime;
else
echo $mydate;

echo " <a href='http://frontpage.klifix.nl/?p=$post->ID'>";
  $shorten_title = truncate($post->post_title, 45);
echo $shorten_title;
  echo '</a>';

$numcomments = $wpdb->get_var("SELECT COUNT(*) FROM dotenel_comments WHERE  comment_post_ID = '{$post->ID}' AND comment_approved = '1'");
echo " ({$numcomments})<br />";

}
?>
<?php endif; ?>

What code do I have to add to this code to show a category-image?