Hi WPyogi,
Many thanks for your reply.
This is a chicken and egg kind of situation, you suggest to backup the site before going on with the image optimizer plugin, but unfortunately we are not able to do that because the images are too large, do you see what I mean.
Is there a way for me to find out if the built-in scale WP option actually works? I suppose I could look into the upload folder and see how large the images actually are.
Regards,
Eugene