vBulletin JavaScript - Collapsing elements

[sebz2009]

At the moment, the Javascript is adding/removing "_collapsed" to an <img> tag for the collapsing of boards.

I want to remove the image element and have most of the images in a single PNG file like

and

do, for example.

I was wondering what I need to change in the JavaScript file to get it to work just in the <a> tag as the image will be in the background of that in the CSS.