Merge 2 PNG-Files without losing alpha channel transparency information

mergePNGs.php

<?php

function mergePNGs($dst_fileURL, $temp_fileURL)
{
  $resolutionX = 1000;
	$resolutionY = 1000;
	$dst_im = imagecreatefrompng($dst_fileURL) or die('Error reading image file');
	$src_im = imagecreatefrompng($temp_fileURL) or die('Error reading image file');
	
	imagealphablending($dst_im, true);
	imagesavealpha($dst_im, true);
	imagealphablending($src_im, true);
	imagesavealpha($src_im, true);
	imagecopy($dst_im, $src_im, 0, 0, 0, 0, $resolutionX, $resolutionY);
	
	header("Content-Type: image/png"); 
	imagePNG($dst_im, $dst_fileURL, 2);
	imagedestroy($dst_im);
	imagedestroy($src_im);
}

?>