Implementation code for php image verification code function to realize distorted characters

/**
* CaptchaImage() - Create a verification code image with distorted characters
* $session_name string The variable name of the Session that needs to be generated when creating the verification code image
* $width int The width of the verification image, default 120, Note: The ratio of image height to width Relatively fixed
* $noise int The number of interferon points, the default is 0
* $disturb int The number of interference characters, the default is 0
* $curve bool Whether to increase the interference curve, the default is true
**/
function CaptchaImage($session_name = '',  $width = 120, $noise = 0, $disturb = 0, $curve = true){
  $im_x = $width;
  $im_y = ceil(0.25 * $width);
  $im = imagecreatetruecolor($im_x, $im_y);
  $text_c = ImageColorAllocate($im, mt_rand(0, 100), mt_rand(0, 100), mt_rand(0, 100));
  $gray_rand = mt_rand(160, 220);
  $buttum_c = ImageColorAllocate($im, $gray_rand, $gray_rand, $gray_rand);
  imagefill($im, 0, 0, $buttum_c);
session_start();
$text = '';
$characters = 'ABCEFGHJKLMNPQRSTUVWXYZ';
for($i = 0, $len = strlen($characters); $i < 4; $i++){
   $text .= $characters{rand(0, $len - 1)};
if(isset($session_name{0}) && session_start()){
   $_SESSION[$session_name] = $text;
   $_SESSION['CaptchaSessionTime'] = time();
}
}
$font = 'arial.ttf';
$size = floor(0.2 * $width);
$ttfbox = imagettfbbox($size, 0, $font, $text);
$text_width = abs($ttfbox[2] - $ttfbox[0]);
$side = floor(($im_x - $text_width) / 2);
$array = array(-1, 1);
for ($i = 0; $i < strlen($text); $i++){
$p = array_rand($array);
$an = $array[$p] * mt_rand(5, 10);      // 字符倾斜角度
imagettftext($im, $size, $an, $side + $i * ($size - 1), $im_y - 3, $text_c, $font, $text{$i});
}
$distortion_im = imagecreatetruecolor ($im_x, $im_y);
imagefill($distortion_im, 0, 0, $buttum_c);
$distortion = floor(0.04 * $width);         // 扭曲程度
for ($i = 0; $i < $im_x; $i++){
for ($j = 0; $j < $im_y; $j++){
$rgb = imagecolorat($im, $i , $j);
if( (int)($i + sin($j / $im_y * 2 * M_PI) * $distortion) <= $im_x && (int)($i + sin($j / $im_y * 2 * M_PI) * $distortion) >= 0 ){
imagesetpixel($distortion_im, (int)($i + sin($j / $im_y * 2 * M_PI - M_PI * 0.1) * $distortion) , $j, $rgb);
}
}
}
if($disturb > 0){
$chars = 'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789';
for($i = 0; $i < $disturb; $i++){
imagestring($distortion_im, 3, mt_rand(-10, $im_x), mt_rand(-10, $im_y), $chars[mt_rand(0, 35)], $text_c);
}
}
//加入干扰象素;
if($noise > 0){
for($i = 0; $i < $noise; $i++){
$randcolor = ImageColorallocate($distortion_im, mt_rand(0,255), mt_rand(0,255), mt_rand(0,255));
imagesetpixel($distortion_im, mt_rand()%$im_x , mt_rand()%$im_y , $randcolor);
}
}
// 加干扰曲线
if($curve){
$rand = mt_rand(5, 30);
$rand1 = mt_rand(15, 25);
$rand2 = mt_rand(5, 10);
for ($yy = $rand; $yy <= $rand + 2; $yy++){
for ($px = -60; $px <= 60; $px++){
$x = $px / $rand1;
$y = ($x != 0) ? sin($x) : $y;
$py = $y * $rand2;
imagesetpixel($distortion_im, $px + 60, $py + $yy, $text_c);
}
}
}
//设置文件头;
Header("Content-type: image/JPEG");
//以PNG格式将图像输出到浏览器或文件;
ImagePNG($distortion_im);
//销毁一图像，释放与image关联的内存;
ImageDestroy($distortion_im);
ImageDestroy($im);
}
CaptchaImage('code', 100); //生成一张图片 并将随机数字存放到key为code的session中