Not sure if it is a bug or just not supported by the feature,
but the word sensor does not replace the words inside URL of images or weblinks.

Why would one wish for such a thing ?
The reason is to be able to block/refuse images with certain content,
to replace words (that often appear in these kind of URL's ) the URL becomes useless and therefore the image won't show.
Maybe it's an idea to create a check box in the word sensor create dialog, which states 'Also on URL'.
This would help very much in preventing spammers posting junk images and links on the forums.

Lambik