ok im not sure if this will work but it mite...
imagestring ($image,5,10,10,'$output = gmstrftime("System uptime is $days Days, %H Hr, %M Min, %S Sec<br>", $c);
',$black);
try change it to..
$output = gmstrftime("System uptime is $days Days, %H Hr, %M Min, %S Sec<br>", $c);
imagestring ($image,5,10,10,$output,$black);