1. Adjust template
Open link-display.tpl, change the top of the file:
<tr>
{if $config.alexa_thumbs}
<td valign="top" style="padding-right: 10px;"><img width="111" height="87" src="http://pthumbnails.alexa.com/image_server.cgi?id=www.esyndicat.com&size=small&u rl={$link.url}" alt="" /></td>
<td valign="top" class="link {$link.status}"{if $link.sponsored AND $config.sponsored_highlight AND $config.sponsored_links} style="background-color: {$config.sponsored_highlight}"{/if}>
{else}
<td colspan="2" class="link {$link.status}"{if $link.sponsored AND $config.sponsored_highlight AND $config.sponsored_links} style="background-color: {$config.sponsored_highlight}"{/if}>
{/if}
to something like this:
<tr>
{if $config.alexa_thumbs}
<td valign="top" style="padding-right: 10px;"><img width="111" height="87" src="http://pthumbnails.alexa.com/image_server.cgi?id=www.esyndicat.com&size=small&u rl={$link.url}" alt="" /></td>
<td valign="top" class="link {$link.status}{if $link.sponsored AND $config.sponsored_highlight AND $config.sponsored_links} sponsored"{/if}>
{else}
<td colspan="2" class="link {$link.status}{if $link.sponsored AND $config.sponsored_highlight AND $config.sponsored_links} sponsored"{/if}>
{/if}
Save changes and close the file.
2. Add an image
Say, the image is bg.gif. Copy this file to templates/<your_template>/img/ folder.
3. Add style
Open css/style.css, and add the following to the bottom of the file:
td.sponsored
{
background-image: url('../img/bg.gif');
}
Save changes and close the file.
Refresh your listing with sponsored links and see what happens.