PHP basic learning: image processing

<?php 
//     图片处理gd2配置文件修改 
?> 
   
<!-- 用图片处理函数画一张图 --> 
<?php 
//     $img = imagecreatetruecolor(500, 500); 
//     $red = imagecolorallocate($img, 255, 0, 0); 
//     $green = imagecolorallocate($img, 0, 255, 0); 
//     $blue = imagecolorallocate($img, 0, 0, 255); 
//     $pur = imagecolorallocate($img, 255, 0, 255); 
//     $yellow = imagecolorallocate($img, 121, 72, 0); 
       
//     imagefilledrectangle($img, 0, 0, 500, 500, $green); 
//     imageline($img, 0, 0, 500, 500, $red); 
//     imageline($img, 500, 0, 0, 500, $blue); 
       
//     imagefilledellipse($img, 250, 250, 200, 200, $yellow); 
       
//     imagefilledellipse($img, 200, 200, 300, 300, $blue); 
       
//     imagejpeg($img, &#39;haha.jpg&#39;); 
//     echo "<img src=&#39;haha.jpg&#39;>"; 
//     imagedestroy($img); 
?> 
   
<!-- 开发验证码(生成验证码) --> 
<?php 
    check_code(); 
    function check_code($width = 100, $height = 50, 
        $num = 4, $type = &#39;jpeg&#39;){ 
        $img = imagecreate($width, $height); 
        $string = &#39;&#39;; 
        for ($i = 0;$i < $num; $i++){ 
            $rand = mt_rand(0, 2); 
            switch ($rand) { 
                case 0: 
                    $ascii = mt_rand(48, 57); 
                    break; 
                case 1: 
                    $ascii = mt_rand(65, 90); 
                    break; 
                case 2: 
                    $ascii = mt_rand(97, 122); 
                    break; 
            } 
            $string .= sprintf(&#39;%c&#39;, $ascii); 
        } 
        imagefilledrectangle($img, 0, 0, $width, $height, randBg($img)); 
        for ($i = 0;$i < 50; $i++){ 
            imagesetpixel($img, mt_rand(0, $width),  
                mt_rand(0, $height), randPix($img)); 
        } 
        for ($i = 0;$i < $num;$i++){ 
            $x = floor($width/$num) * $i + 2; 
            $y = mt_rand(0, $height - 15); 
               
            imagechar($img, 5, $x, $y, $string[$i], randPix($img)); 
        } 
           
        $func = &#39;image&#39; . $type; 
        $header = &#39;Content-type:image/&#39;.$type; 
        if (function_exists($func)) { 
            header($header); 
            $func($img); 
        }else { 
           echo &#39;图片类型不支持&#39;;  
        } 
        imagedestroy($img); 
        return $string; 
    } 
    function randBg($img){ 
        return imagecolorallocate($img, mt_rand(130, 255), 
            mt_rand(130, 255), mt_rand(130, 255)); 
    } 
    function randPix($img){ 
        return imagecolorallocate($img, mt_rand(0, 120),  
            mt_rand(0, 120), mt_rand(0, 120)); 
    } 
?>  
<!-- 图像缩放和剪裁技术 --> 
<?php 
    $image = imagecreatefrompng(&#39;fbb.png&#39;); 
       
    $percent = 0.1; 
    list($width, $height) = getimagesize(&#39;fbb.png&#39;); 
       
    $new_width = $width * $percent; 
    $new_height = $height * $percent; 
       
    $new_image = imagecreatetruecolor($new_width, $new_height); 
    imagecopyresampled($new_image, $image, 0, 0, 
        0, 0, $new_width, $new_height, $width, $height); 
    header(&#39;content-type:image/jpeg&#39;); 
    imagejpeg($new_image); 
?> 
<!-- 图片水印处理 --> 
<?php 
    $dst = imagecreatefrompng(&#39;https://img.php.cn/upload/course/000/ 
        000/002/5833ebba648cf229.png&#39;); 
    $src = imagecreatefrompng(&#39;https://img.php.cn/ 
        upload/course/000/000/002/5833ebe90cc11285.png&#39;); 
    $dst_info = getimagesize(&#39;5833ebba648cf229.png&#39;); 
    $src_info = getimagesize(&#39;5833ebe90cc11285.png&#39;); 
       
    $dst_x = $dst_info[0] - $src_info[0]; 
    $dst_y = $dst_info[1] - $src_info[1]; 
    imagecopymerge($dst, $src, $dst_x, $dst_y, 0, 0,  
        $src_info[0], $src_info[1], 100); 
    header(&#39;Content-type:image/png&#39;); 
    imagepng($dst); 
    imagedestroy($dst); 
    imagedestroy($src); 
?>   
<!-- 做一个智能的图片水印函数 --> 
<?php        
?>