Stuff

       $uploadedimg = imagecreatefromjpeg("./images/uploaded/$picname");

       $previewimg = imagecreatetruecolor($previewx, $previewy);
       imagecopyresized($previewimg, $uploadedimg, 0, 0, 0, 0, $previewx, $previewy, $picx, $picy);
       imagealphablending($previewimg, true);

       $watermarkimg = imagecreatefrompng("./images/watermark.png");
       $bgcol = imagecolorallocate($watermarkimg, 255, 255, 255);
       imagecolortransparent($watermarkimg, $bgcol);

       $watermarkx = (round($previewx / 2) - 150);
       $watermarky = (round($previewy / 2) - 150);
       imagecopymerge($previewimg, $watermarkimg, $watermarkx, $watermarky, 0, 0, 300, 300, 10);
       imagejpeg($previewimg, "./images/preview/$picname", 100);