Simple PHP Image Watermark

Have you ever wanted to add an alpha-transparent watermark to an image that you post on your website?
Here is a simple PHP script that watermarks JPEG and PNG images.
<?php
function watermark($sourcefile, $watermarkfile) {
# $sourcefile = Filename of the picture to be watermarked.
# $watermarkfile = Filename of the 24-bit PNG watermark file.
//Get the resource ids of the pictures
$watermarkfile_id = imagecreatefrompng($watermarkfile);
imageAlphaBlending($watermarkfile_id, false);

imageSaveAlpha($watermarkfile_id, true);

$fileType = strtolower(substr($sourcefile, strlen($sourcefile)-3));

switch($fileType) {
case("gif"):
$sourcefile_id = imagecreatefromgif($sourcefile);
break;

case("png"):
$sourcefile_id = imagecreatefrompng($sourcefile);
break;

default:
$sourcefile_id = imagecreatefromjpeg($sourcefile);
}

//Get the sizes of both pix
$sourcefile_width = imageSX($sourcefile_id);
$sourcefile_height = imageSY($sourcefile_id);
$watermarkfile_width = imageSX($watermarkfile_id);
$watermarkfile_height = imageSY($watermarkfile_id);

$dest_x = ( $sourcefile_width / 2 ) - ( $watermarkfile_width / 2 );
$dest_y = ( $sourcefile_height / 2 ) - ( $watermarkfile_height / 2 );

// if a gif, we have to upsample it to a truecolor image
if($fileType == "gif") {
// create an empty truecolor container
$tempimage = imagecreatetruecolor($sourcefile_width, $sourcefile_height);

// copy the 8-bit gif into the truecolor image
imagecopy($tempimage, $sourcefile_id, 0, 0, 0, 0, $sourcefile_width, $sourcefile_height);// copy the source_id int
$sourcefile_id = $tempimage;
}
imagecopy($sourcefile_id, $watermarkfile_id, $dest_x, $dest_y, 0, 0, $watermarkfile_width, $watermarkfile_height);
//Create a jpeg out of the modified picture
switch($fileType) {
// remember we do not need gif any more, so we use only png or jpeg.
// See the code above to see how we handle gifs
case("png"):
header("Content-type: image/png");
imagepng ($sourcefile_id);
break;

default:
header("Content-type: image/jpg");
imagejpeg ($sourcefile_id);
}
imagedestroy($sourcefile_id);
imagedestroy($watermarkfile_id);
}
watermark("main.jpg","watermark.png");
?>

Sample output below...No comment on the picture pls... its sacred y know..

main.jpg

watermark.png

watermarked output jpeg