Here's an example of how the Co-Authors plugin may be used along with the User Photo plugin:
$c = new CoAuthorsIterator();
print '<ol class="' . ($c->count() == 1 ? 'single' : 'multiple') . '">';
while($c->iterate()){
print '<li>';
print "<a href='" . get_author_posts_url($authordata->ID) . "'>";
if(function_exists('userphoto_the_author_thumbnail'))
userphoto_the_author_thumbnail('', '<br />');
the_author();
print '</a></li>';
}
print '</ol>';