Are you using class "folder" for each object heading? Where do you want to add the image, in the folder.tpl or in another template?
If you add a datatype image to your folder class in setup/classes:edit/content:folder you can add your own image to each object that will show where you want in your folder.tpl template file and thus get the unique image display as you described. You can then modify the image in image.ini.append.php found in settings/siteaccess/<siteacces_name>/image.ini.append.php.
