Captcha validation in PHP

Question

I used the following code to create Captcha to my form. Captcha creating well. Now I want to change font-size, and Font character spaces. I don't know how to change in the following code.

      <?php
             session_start();
             $code= substr(str_shuffle("abcdefghijklmnopqrstuvwxyz"), 0, 6);
             $_SESSION["code"]=$code;
             $im = imagecreatetruecolor(150, 35);
             $bg = imagecolorallocate($im, 255, 255, 255);
             $fg = imagecolorallocate($im, 0, 0, 0);
             imagefill($im, 5, 5, $bg);
             imagestring($im, 5, 8, 8,  $code, $fg);
             header("Cache-Control: no-cache, must-revalidate");
             header('Content-type: image/png');
             imagepng($im);
             imagedestroy($im);
        ?>

Answer 1

You can use the code below to implement a simple captcha using gd library of PHP. As you are beginner, here is a sample code for quick testing, it covers font-sizing also:

<?php
session_start();
header('Content-type: image/jpeg');

$text = rand(1000, 9999);
$font_size = 30;

$image_width = 200;
$image_height = 40;

$image = imagecreate($image_width, $image_height);
imagecolorallocate($image, 255, 255, 255);
$text_color = imagecolorallocate($image, 0, 0, 0);

for ($x=1; $x<=40; $x++) {
     $x1 = rand(1, 100);
     $y1 = rand(1, 100);
     $x2 = rand(1, 100);
     $y2 = rand(1, 100);

 imageline($image, $x1, $y1, $x2, $y2, $text_color);
}

imagettftext($image, $font_size, 0, 15, 30, $text_color, 'FREESCPT.ttf', $text);
imagejpeg($image);

?>

In imagettftext function:

imagettftext($image, $font_size, $angle, $x, $y, $text_color, '$font-family', $text);

  $image is the $imagecreate function
  $font_size is the size of font you want.
  $angle is the angle of the fonts tilted
  $x and $y are coordinates.
  $text_color is the imagecolorallocate function
  $font-family is the family of font you want to use
  $text is the text or random text to be displayed

Here is the good tutorial on how to build captcha in php -> link

Answer 2

you can change font using imagestring function