What is wrong with this ?

ok i have this function for adding a watermark on another image .. i got the image ... + the watermark and keeps giving me blank screen or that is done but actually nothing is done ..

<?PHP 
function applyWatermark( $srcFilename, $dstFilename, $wtrFilename, $wtrTransparency )
{
	 $use_gd = true ;
	 $COMPOSITE= "0";
	 $gdInstalled = true;

	// input validation
	$wtrTransparency = (int) $wtrTransparency;
	if ( $wtrTransparency > 100 )
		$wtrTransparency = 100;
	if ( !file_exists( $srcFilename ) )
		return IMAGE_ERROR_SOURCE_NOT_EXISTS;
	if ( !file_exists( $wtrFilename ) )
		return IMAGE_ERROR_SOURCE_NOT_EXISTS;

	// if destination and source filenames are equivalent then change mode for destination
	if ( $srcFilename == $dstFilename )
		chmod( $dstFilename, 0666 );

	if ( $use_gd )
	{
		if ( !$gdInstalled )
			return IMAGE_ERROR_GD_NOT_INSTALLED;
		$gdInfoArray = gd_info();
		$size = getimagesize( $srcFilename );
		$wtrSize = getimagesize( $wtrFilename );

		// only GIF, JPG and PNG allowed
		switch ( $size[2] )
		{
			case IMAGE_TYPE_GIF:
				if ( !$gdInfoArray['GIF Read Support'] || !$gdInfoArray['GIF Create Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$src_im = imagecreatefromgif( $srcFilename );
				break;
			case IMAGE_TYPE_JPG:
				if ( !$gdInfoArray['JPG Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$src_im = imagecreatefromjpeg( $srcFilename );
				break;
			case IMAGE_TYPE_PNG:
				if ( !$gdInfoArray['PNG Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$src_im = imagecreatefrompng( $srcFilename );
				break;
			default:
				return IMAGE_ERROR_WRONG_TYPE;
		}
		switch ( $wtrSize[2] )
		{
			case IMAGE_TYPE_GIF:
				if ( !$gdInfoArray['GIF Read Support'] || !$gdInfoArray['GIF Create Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$wtr_im = imagecreatefromgif( $wtrFilename );
				break;
			case IMAGE_TYPE_JPG:
				if ( !$gdInfoArray['JPG Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$wtr_im = imagecreatefromjpeg( $wtrFilename );
				break;
			case IMAGE_TYPE_PNG:
				if ( !$gdInfoArray['PNG Support'] )
					return IMAGE_ERROR_GD_TYPE_NOT_SUPPORTED;
				$wtr_im = imagecreatefrompng( $wtrFilename );
				break;
			default:
				return IMAGE_ERROR_WRONG_TYPE;
		}

		if ( !$src_im || !$wtr_im )
			return IMAGE_ERROR_GD_OPEN_FAILED;

		$watermarkX = ($size[0] - $wtrSize[0]) / 2;
		$watermarkY = $size[1] - $wtrSize[1];

		$mergeResult = imagecopymerge( $src_im, $wtr_im, $watermarkX, $watermarkY, 0, 0,
			$wtrSize[0], $wtrSize[1], $wtrTransparency );

		if ( !$mergeResult )
			return IMAGE_ERROR_GD_MERGE_ERROR;

		switch ( $size[2] )
		{
			case IMAGE_TYPE_GIF:
				$writeResult = imagegif( $src_im, $dstFilename );
				break;
			case IMAGE_TYPE_JPG:
				$writeResult = imagejpeg( $src_im, $dstFilename );
				break;
			case IMAGE_TYPE_PNG:
				$writeResult = imagepng( $src_im, $dstFilename );
				break;
		}

		// free memory
		imagedestroy( $src_im );
		imagedestroy( $wtr_im );

		if ( $writeResult )
			return IMAGE_ERROR_SUCCESS;
		else
			return IMAGE_ERROR_GD_WRITE_FAILED;
	}
	else
	{
		$imgTransparency = 100 - $wtrTransparency;
		$cmd = "$COMPOSITE -gravity \"South\" -dissolve $imgTransparency $wtrFilename -dissolve $wtrTransparency $srcFilename $dstFilename";
		@exec( $cmd );
		if ( file_exists($dstFilename) )
			return IMAGE_ERROR_SUCCESS;
		else
			return IMAGE_ERROR_IMAGEMAGICK_ERROR;
	}
}
			$srcfile = './pic.jpg' ;
			$logo = './watermark.png' ;
			$srcfile2= './pic2.jpg';
			$tr = '10';
		applyWatermark( $srcfile, $srcfile,$logo, $tr );

echo "done" ;




?>

Code (markup):

 

try putting error_reporting(E_ALL); at the beginning of the file and see if you get any errors

 

again .. blank screen . + my errors are turned on by default ..

 

I noticed an interesting comment on the PHP manual page for imagecopymerge. Apparently, it can't handle the alpha channel in PNGs, so someone wrote a function to fix it.
http://au.php.net/manual/en/function.imagecopymerge.php#88456