如何使用 PHP 内置函数处理图像？

<?php
$src_image = 'image.jpg';
$dst_image = 'image-scaled.jpg';
$scaled_width = 300;
$scaled_height = 200;

$src = imagecreatefromjpeg($src_image);
$dst = imagecreatetruecolor($scaled_width, $scaled_height);
imagecopyresampled($dst, $src, 0, 0, 0, 0, $scaled_width, $scaled_height, imagesx($src), imagesy($src));
imagejpeg($dst, $dst_image);
?>

<?php
$src_image = 'image.jpg';
$dst_image = 'image-cropped.jpg';
$crop_x = 100;
$crop_y = 200;
$crop_width = 300;
$crop_height = 200;

$src = imagecreatefromjpeg($src_image);
$dst = imagecrop($src, ['x' => $crop_x, 'y' => $crop_y, 'width' => $crop_width, 'height' => $crop_height]);
imagejpeg($dst, $dst_image);
?>

<?php
$main_image = 'image.jpg';
$watermark_image = 'watermark.png';
$output_image = 'image-with-watermark.jpg';
$margin = 50;

$main = imagecreatefromjpeg($main_image);
$watermark = imagecreatefrompng($watermark_image);

$watermark_width = imagesx($watermark);
$watermark_height = imagesy($watermark);

$dst_x = imagesx($main) - $margin - $watermark_width;
$dst_y = imagesy($main) - $margin - $watermark_height;

imagecopymerge($main, $watermark, $dst_x, $dst_y, 0, 0, $watermark_width, $watermark_height, 75);
imagejpeg($main, $output_image);
?>