Problem resizing images

[SBro]

I have the following script which resizes and watermarks images, it all works fine, however when I add the line to only resize if required, the outputted image is just a black image with the watermark, anyone know why this is, and how I get around it? I assume it's because my script needs to execute imagecopyresampled() for some reason for the watermarking to work, and thus when it is not executed, I get a black (watermarked) image, thanks.

function watermark($images, $max, $quality, $wmark) {
		foreach ($images as $img) {
			// get sizes
			list ($orig_width, $orig_height) = getimagesize($img);
			list ($width, $height) = $this->get_sizes($orig_width, $orig_height, $max);

		// original
		$image_p = imagecreatetruecolor($width, $height);
		$image = imagecreatefromjpeg($img);

		// resize if required
		if ($orig_width > $width) imagecopyresampled($image_p, $image, 0, 0, 0, 0, $width, $height, $orig_width, $orig_height);

		// watermark details
		$watermark = imagecreatefrompng($wmark); 
		$watermark_width = imagesx($watermark);  
		$watermark_height = imagesy($watermark);  

		// where to place watermark
		$dest_x = $width - $watermark_width - 5;  
		$dest_y = $height - $watermark_height - 5;  

		// create watermark
		if (!imagecopymerge($image_p, $watermark, $dest_x, $dest_y, 0, 0, $watermark_width, $watermark_height, 100)) {
			// error
			error::log(ERR_MED, 'Resizing and watermarking of '.$img.' unable to be completed.', ERR_SHOW);  
			exit();
		}
		imagejpeg($image_p, $img, $quality);

		// destroy
		imagedestroy($image_p);  
		imagedestroy($watermark);
	}
}