Aye, CORS settings will break it, as will any images that get dynamically updated our loaded as you scroll etc. Also it won't catch images used as backgrounds.

Aye, CORS settings will break it, as will any images that get dynamically updated our loaded as you scroll etc. Also it won't catch images used as backgrounds. There are a lot of ways to break bookmarklets, intentionally, by application of security settings for other reasons (like, erm, security!), or accidentally.