good but i have some suggestions Rated 4 out of 5 stars
1. Regular expressions in place of exact site address: this will help allow/block content delivered from cdn's where the sub-domains are used. It may lead to unexpected behavior if user types a bad regex, but you can have this as an advanced settings defaulting to exact website url. This may to some extent solve #alalal011's problems.
2. As #jaminga suggested, having some kind of shortcut to enable disable images for the current tab. This would be excellent.
3. The button on the address bar either disables/enables images for all websites. You could have a small drop-down next to it with options to specify whether it should be all websites or just current website.