Captcha in html form

I have a html form and i have written the necessary code.

html in main code:

<p id="formele" style="height:125px;">
<img src="captcha_code_file.php?rand=<?php echo rand(); ?>" style="width:200px;height:50px;"id='captchaimg' ><br>
<label for='message'>Enter captcha here :</label><br>
<input id="6_letters_code" style="background-color:lightblue; height : 25px;" name="6_letters_code" type="text" required /><br>
</p>

php in main code:

if(empty($_SESSION['6_letters_code'] ) ||
        strcasecmp($_SESSION['6_letters_code'], $_POST['6_letters_code']) != 0)
                        {
        //Note: the captcha code is compared case insensitively.
        //if you want case sensitive match, update the check above to
        $err=1;
        echo "<p style='color:red;'>nCaptcha code <em> DOES NOT MATCH</em>!! Press backspace and re-enter captcha</p>";
        echo "<p style='color:blue;'>Please re-enter password also(because password will be erased).<hr>";
        }

And my captcha_code_file.php code(downloaded):

<?php
session_start();
//Settings: You can customize the captcha here
$image_width = 200;
$image_height = 50;
$characters_on_image = 6;
$font = './monofont.ttf';

//The characters that can be used in the CAPTCHA code.
//avoid confusing characters (l 1 and i for example)
$possible_letters = '23456789bcdfghjkmnpqrstvwxyz';
$random_dots = 0;
$random_lines = 20;
$captcha_text_color="0x142864";
$captcha_noice_color = "0x142864";

$code = '';


$i = 0;
while ($i < $characters_on_image) { 
$code .= substr($possible_letters, mt_rand(0, strlen($possible_letters)-1),     1);
$i++;
}


$font_size = $image_height * 0.75;
$image = @imagecreate($image_width, $image_height);


/* setting the background, text and noise colours here */
$background_color = imagecolorallocate($image, 255, 255, 255);

$arr_text_color = hexrgb($captcha_text_color);
$text_color = imagecolorallocate($image, $arr_text_color['red'], 
    $arr_text_color['green'], $arr_text_color['blue']);

$arr_noice_color = hexrgb($captcha_noice_color);
$image_noise_color = imagecolorallocate($image, $arr_noice_color['red'], 
    $arr_noice_color['green'], $arr_noice_color['blue']);


/* generating the dots randomly in background */
for( $i=0; $i<$random_dots; $i++ ) {
imagefilledellipse($image, mt_rand(0,$image_width),
 mt_rand(0,$image_height), 2, 3, $image_noise_color);
}


/* generating lines randomly in background of image */
for( $i=0; $i<$random_lines; $i++ ) {
imageline($image, mt_rand(0,$image_width), mt_rand(0,$image_height),
 mt_rand(0,$image_width), mt_rand(0,$image_height), $image_noise_color);
}


/* create a text box and add 6 letters code in it */
$textbox = imagettfbbox($font_size, 0, $font, $code); 
$x = ($image_width - $textbox[4])/2;
$y = ($image_height - $textbox[5])/2;
imagettftext($image, $font_size, 0, $x, $y, $text_color, $font , $code);


/* Show captcha image in the page html page */
header('Content-Type: image/jpeg');// defining the image type to be shown in browser widow
imagejpeg($image);//showing the image
imagedestroy($image);//destroying the image instance
$_SESSION['6_letters_code'] = $code;

function hexrgb ($hexstr)
{
$int = hexdec($hexstr);

return array("red" => 0xFF & ($int >> 0x10),
           "green" => 0xFF & ($int >> 0x8),
           "blue" => 0xFF & $int);
}
?>

The catcha image is not appearing in my web page. How can i fix this? I’m pretty sure there is no problem with the downloaded code.

Answer

I simply use already tested and working scripts which when dealing with captcha in php, you can refer links below, it will serve basic purpose of captcha.

http://99webtools.com/blog/php-simple-captcha-script/

http://www.abeautifulsite.net/a-simple-php-captcha-script/