[Lynne]

In the postbit template (if you user info is on top) or the postbit_legacy template (if your user info is to the left), find:

<if condition="$post['joindate']"><div>$vbphrase[join_date]: $post[joindate]</div></if>

Add above it:

<if condition="is_member_of($post, x, y, z)">
<a href="link.php"><img src="image.jpg"></a>
</if>

And that should show a linked image for the user of a post who is in usergroup x, y, or z