This is just an idea, Im not sure if it will work, since I havent tested it out myself, but Ive used it on other systems not related to smarty, it might help you out:
On the file /skin1/customer/categories.tpl
On line 5, just after {section name=cat_num loop=$categories}, insert this line:
{ $icons[cat_num].image }
Now if it is on the file system, this would be:
<img src={ $icons[cat_num].image_path } width="20" border="0" align="left">
Im just learning Smarty, so this is something that needs to be tested, backup the file first, before you try it out.