I know that other people are experiencing a similar problem.
When I try to Smush my images, I got an error saying:
ERROR: http://www.mywebsite.com/assets/media/2013/09/myimage.jpg must be within the website home URL (http://www.positive-magazine.com/mywordpressfolder)
For security reasons I use a secret folder inside my server for all the WordPress files, while using an outside folder (assets) for uploads of media files. Unfortunately Smash.It can't do its work due to this reason.
Is there any fix coming someday? I experienced this thing many months ago yet when I first tried the plugin.