//first get the current category ID
$cat_id = get_query_var('cat');
//then i get the data from the database
$cat_data = get_option("category_$cat_id");
//and then i just display my category image if it exists
if (isset($cat_data['img'])){
echo '<div class="category_image"><img src="'.$cat_data['img'].'"></div>';
}