Proper way to remove all metadata from an image

cleanup.php

<?php

$img = new Imagick($img);

// code by Max Eremin http://php.net/manual/en/imagick.stripimage.php#120380

// we need to keep the ICC profiles
$profiles = $img->getImageProfiles('icc', true);

// but remove everything else
$img->stripImage();

// re-attach the color profiles
if ( ! empty($profiles)) {
    $img->profileImage('icc', $profiles['icc']);
}

Dont know why, but half my images increase in size after stripping the meta data

In file size, or dimensions?

If you can, post a link to one of the images so that we can inspect it closer. Also post the version of your php/imagemagick as this code snippet is very old, perhaps something changed recently...

Just thought of something: This process is re-compressing the image, and the default quality is set pretty high, 92 IIRC, so that could be the reason why you're getting bigger images. It's best that you set the quality down to the actual quality of the original image or the value that you want:

$img->setImageCompressionQuality($realQuality);