PHP - Detect if image has been manually rotated, EXIF Orientation flag wrong - php

Question

I’m experiencing some strange issues with image rotation.
Originally we were having the problem of some users uploading images onto our site but they were appearing the wrong way around. We therefore wanted to implement some code to check the EXIF Orientation flag and rotate the image if necessary.
Here is what the simplified function looks like:
function image_fix_orientation($filename) {
$exif = exif_read_data($filename);
if (!empty($exif['Orientation'])) {
$image = imagecreatefromjpeg($filename);
switch ($exif['Orientation']) {
case 3:
$image = imagerotate($image, 180, 0);
break;
case 6:
$image = imagerotate($image, -90, 0);
break;
case 8:
$image = imagerotate($image, 90, 0);
break;
}
imagejpeg($image, $filename, 100);
}
}
This seems to work fine for the images which have the Orientation flag set, were rotated and causing the original issue.
However, bizarrely I have found a number of images previously uploaded onto our server (we retain the original image with EXIF data intact) from before we have implemented the above code which appear to contain an Orientation flag (of say ‘3’) but their raw picture is the correct way up. If I feed one of these images into my new upload code it reads the Orientation flag and rotates the image, but the image was the correct way around to begin with.
I believe the user has likely manually rotated the image prior to upload yet it’s still retaining the Orientation flag value. For example, if I rotate an image in Paint it seems to retain the same Orientation value. Here is an example image http://s16.postimg.org/cv5ejchqt/exig.jpg (arrow points to the true top of the image), yet it has the Orientation flag value of 3 so is rotated when using my new upload code.
Is there a way to detect if the user has manually rotated, somehow?
Thanks