Thanks James, are you aware of any extension that can help me with that? Cropping the image to make it more rectangular when in full screen would be fine for me.
Well since anyone gave any tip, just followed another path. Instead of making a hook with wordpress. I just configured my mail server to use the same passwords than wordpress.
Since wordpress is using the “standard” phpass framework to create the password hashes i can be validated with any of the standard methods (https://www.openwall.com/phpass/)
