How to use image in widget title?

Hi there, you can see an example of a site page here:

As you can see, the twitter plugin has an image of the twitter logo by default.

I'd like to use this facebook logo above the facepile:

Unfortunately, when I enter the img src HTML tag in the widget title and save, the stuff I entered disappears. I also can't just add it into a separate Text widget above as my theme automatically adds in the dividers between widgets.

Any ideas how I can achieve this?