Description:
------------
rand() weakness.

example (reproduce code): rand generate pattern instead of noise

Reproduce code:
---------------
<?
 $i=imagecreatetruecolor(1024,768);

 for($y=0;$y<768;$y++){
  for($x=0;$x<1024;$x++){
   $c=rand(0,1)*255;
   imagesetpixel($i,$x,$y,($c<<16)+($c<<8)+$c);
  }
 }

 header('Content-type: image/png');
 imagepng($i);
?>

Expected result:
----------------
noise

Actual result:
--------------
pattern