Seminar for Joomla has been released as GPL. However, the author, for some unknown reason, has decided to scramble the code so it's basically impossible to modify the code. This is not what the GPL licence was intended for.

The code is half written in German and the support site in German also.

As there is no support whatsoever and in respect of the foul play code scrambling, to remove the copyright notice....
Line 1064 , seminar.class.php , located in /components/com_seminar


LOCATE THIS LINE (1024)
$html = "<center><table><tr><td class=\"sem_footer\"><img src=\"".sem_f006()."menulogo.png\" border='0' style=\"vertical-align:middle\"> <i><a href=\"seminar.vollmar.ws\" target=\"_new\">".JTEXT::_('SEM_0043')."</a> V".sem_f001()."</i> &#169; &#68;&#105;&#114;&#107; &#86;&#111;&#108;&#108;&#109;&#97;&#114; ".date("Y")."</td></tr></table></center>";


DELETE IT

or add // at the front and + at the end.