This GDlib Trick let you stack different transparent png Images to one.

stack_pngs.php

<?php

$image_arr=array('path1.png', 'path2.png', 'path3.png');
echo gd_gen_image($image_arr);


function gd_gen_image($arr){
	$base  = imagecreatetruecolor(913, 500);
	$color = imagecolorallocatealpha($base, 0, 0, 0, 127);
	imagefill($base, 0, 0, $color);
	imagesavealpha($base, TRUE);
  
	foreach($arr as $key=>$image_val){
		$this_layer=imageCreateFromPNG($image_val);
		ImageCopy ( $base, $this_layer, 0 , 0 , 0 , 0 , 913 , 500 );
	}

	// Begin capturing the byte stream
	ob_start();
		imagePNG($base);
	$out=ob_get_clean();
	// END capturing the byte stream
	return "<img src='data:image/png;base64," . base64_encode( $out ) . "' />";
}

?>