how to create a wave image by PHP(GD)

imagewave.php

<?php
/**
 * @param resource $img
 * @param int $width
 * @param int $height
 * @param int $period
 * @param int $amplitude
 * @return resource
 */
function imageWave($img, $width, $height, $period = 10, $amplitude = 5) {
	$p = $period * rand(1, 3);
	$k = mt_rand(0, 100);
	for ($i = 0; $i<$width; $i++) {
		imagecopy($img, $img, $i-1, sin($k+$i/$p) * $amplitude, $i, 0, 1, $height);
	}
	$k = mt_rand(0,100);
	for ($i = 0; $i<$height; $i++) {
		imagecopy($img, $img, sin($k+$i/$p) * $amplitude, $i-1, 0, $i, $width, 1);
	}
	return $img;
}

$img = imagecreatefromjpeg("test.jpg");
$img = imageWave($img, imagesx($img), imagesy($img));
imagejpeg($img, "out.jpg");