Add image to sidebar on Wordpress blog

I want to add a small picture to my Wordpress blog sidebar www.25to30.co.uk.

Image is attached. It shall need to be re-sized, you'll need to work out the correct dimensions so that it fits neatly in to the side bar.

I understand that it is simply a case of adding the image to the media library and then adding the image URL with appropriate html code to a custom text widget but for some reason I'm struggling to do this.

I'd like this done immediately.