In newer versions of PHP, due to incorrect syntax for the imagejpeg function in transformation_wrapper.php, image resizing breaks (outputs no image data).
The line that reads:
ImageJPEG($destImage, '', 75);
ImageJPEG($destImage, NULL, 75);
as per the documentation at http://php.net/manual/en/function.imagejpeg.php .
The current way works fine on my server with PHP 5.3.8, but not on my server with PHP 5.4.6, but I'm not sure on the exact version cutoff.