Disable BBcodes in a certain theme?

On my old vb3 board, I had a plug-in (that I can't seem to find) that disabled the IMG tag for a single theme. I have a work-safe theme that my members really like, which has no avatars, no images in posts and a generic looking header so that they can browse my guitar forum incognito at work. (Because let's face it, guitar forums are more fun than actually working.)

How do I pull this off with vb4? I've already stripped the theme of all the usual bits, but I don't know how to stop it from parsing the IMG bbcode (and ideally the VIDEO bbcode as well).

Any insight would be great. Thanks!