for($x=1;$x<=255;$x++) {
    echo chr($x) . "&nbsp;";
}

<?php
   // Set the content-type
   header('Content-Type: image/png');

   // Create the image
   $im = imagecreatetruecolor(400, 30);

   // Create some colors
   $white = imagecolorallocate($im, 255, 255, 255);
   $grey = imagecolorallocate($im, 128, 128, 128);
   $black = imagecolorallocate($im, 0, 0, 0);
   imagefilledrectangle($im, 0, 0, 399, 29, $white);

   // The string with character sets
   for($i=0; $i<256; $i++){
        $text.= chr($i);
   }

   // Replace path by your own font path
   $font = 'arial.ttf';

   // Add some shadow to the text
   imagettftext($im, 20, 0, 11, 21, $grey, $font, $text);

   // Add the text
   imagettftext($im, 20, 0, 10, 20, $black, $font, $text);

   // Using imagepng() results in clearer text compared with imagejpeg()
   imagepng($im);
   imagedestroy($im);
?>