I activated and come to the option. After the update, it seems that there is nothing changes as I move over my image it still says "image" - no new alt tag was applied.
Is it supposed to do sth else after the activation?
Thank you for this very useful tool
http://wordpress.org/extend/plugins/seo-image/
Alt is the text that is displayed when an image can not be found(It's also a good place to put keywords *wink**wink*), the title is the rollover text, I'm pretty sure you would still have to manually have to change the alt and title tags for the pictures posted before the plugin was installed.