Hola encontre el archivo log y los errores son bastente
[28-Oct-2012 15:19:25] PHP Warning: imagecreatefrompng(images/captcha.png) [<a href='function.imagecreatefrompng'>function.imagec reatefrompng</a>]: failed to open stream: No such file or directory in /home/u171863611/public_html/comentarios/caputcha.php on line 19
[28-Oct-2012 15:19:25] PHP Warning: imagecolorallocate(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 23
[28-Oct-2012 15:19:25] PHP Warning: imagecolorallocate(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 27
[28-Oct-2012 15:19:25] PHP Warning: getimagesize(images/captcha.png) [<a href='function.getimagesize'>function.getimagesize </a>]: failed to open stream: No such file or directory in /home/u171863611/public_html/comentarios/caputcha.php on line 31
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imageline(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 40
[28-Oct-2012 15:19:25] PHP Warning: imagettftext() expects parameter 1 to be resource, boolean given in /home/u171863611/public_html/comentarios/caputcha.php on line 47
[28-Oct-2012 15:19:25] PHP Warning: imagepng(): supplied argument is not a valid Image resource in /home/u171863611/public_html/comentarios/caputcha.php on line 55