Convert html to bbcode in existing posts

[asabet]

I have a forum where members have posted tons of images from Flickr in the past using html which Flickr provided prior to making bbcode available. If I disable html on that forum, all those images get broken.

Here is an example:

<a href="http://www.flickr.com/photos/bzhou/4872039026/" title="P1000074 by bzhou, on Flickr"><img src="http://farm5.static.flickr.com/4143/4872039026_7283ba5506_z.jpg" width="640" height="640" alt="P1000074" /></a>

I noticed that if I open the posts to edit them and click that button that switches editor to source mode, it automatically converts them to BBcode. Is there a way to do that for all posts without going one by one by hand?