In a template you can use something like:
Code:
<vb:if condition="is_member_of($bbuserinfo, 4)">
<img src="group4.gif">
<vb:elseif condition="is_member_of($bbuserinfo, 5)" />
<img src="group5.gif">
<vb:elseif condition="is_member_of($bbuserinfo, 6)" />
<img src="group6.gif">
</vb:if>
and of course you can extend that to as many as you want.
And if you only want to specify a special image for certain groups, you could have a "catch-all" by ending with an "else", like:
Code:
...
<vb:elseif condition="is_member_of($bbuserinfo, 6)" />
<img src="group6.gif">
<vb:else />
<img src="others.gif">
</vb:if>