captcha.php

<?php
session_start();
$permitted_chars = 'ABCDEFGHJKLMNPQRSTUVWXYZ';

function generate_string($input, $strength = 10) {
    $input_length = strlen($input);
    $random_string = '';
    for($i = 0; $i < $strength; $i++) {
        $random_character = $input[mt_rand(0, $input_length - 1)];
        $random_string .= $random_character;
    }
    return $random_string;
}
$image = imagecreatetruecolor(200, 50);
imageantialias($image, true);
$colors = [];
$red = rand(125, 175);
$green = rand(125, 175);
$blue = rand(125, 175);
for($i = 0; $i < 5; $i++) {
    $colors[] = imagecolorallocate($image, $red - 20*$i, $green - 20*$i, $blue - 20*$i);
}
imagefill($image, 0, 0, $colors[0]);
for($i = 0; $i < 10; $i++) {
    imagesetthickness($image, rand(2, 10));
    $line_color = $colors[rand(1, 4)];
    imagerectangle($image, rand(-10, 190), rand(-10, 10), rand(-10, 190), rand(40, 60), $line_color);
    imagearc($image, rand(-10, 190), rand(-10, 10), rand(-10, 190), rand(40, 60), rand(-10, 190), rand(-10, 10), $line_color);
}
$black = imagecolorallocate($image, 0, 0, 0);
$white = imagecolorallocate($image, 255, 255, 255);
$textcolors = [$black, $white];
$fonts = [dirname(__FILE__).'//fonts/Aloevera.ttf', dirname(__FILE__).'//fonts/SketchBook.ttf', dirname(__FILE__).'//fonts/MontserratSemibold.ttf', dirname(__FILE__).'//fonts/FeelfreePersonalUseRegular.ttf'];
$string_length = 4;
$captcha_string = generate_string($permitted_chars, $string_length);
$_SESSION['captcha'] = $captcha_string;
for($i = 0; $i < $string_length; $i++) {
    $letter_space = intval(170/$string_length);
    $initial = 15;
    imagettftext($image, 24, rand(-15, 15), $initial + $i*$letter_space, rand(25, 45), $textcolors[rand(0, 1)], $fonts[array_rand($fonts)], $captcha_string[$i]);
}
header('Content-type: image/png');
imagepng($image);
imagedestroy($image);
?>