[Andreas]

In profile.php find

PHP Code:

if ($vboptions['maximages'] != 0) 


ABOVE that ADD

PHP Code:

if (!is_member_of($bbuserinfo, 20) AND fetch_character_count($signature, '[img') > 0)
{
    $preview = 'true';  
    $errors[] = 'Sorry, but you are not allowed to use images in your signature';
} 


FIND

PHP Code:

if ($_REQUEST['do'] == 'editsignature')
{ 


BELOW that ADD

PHP Code:

if (!is_member_of($bbuserinfo, 20))
{
    $vboptions['allowbbimagecode'] = false; 
} 


Then only users in usergroup 20 should be able to use images.