You want to link that logo of The National Council for Hypnotherapy ?
Its easy HTML code :
<a href="http://www.hypnotherapists.org.uk/" target="_blank">
<img src="http://www.hypnotherapists.org.uk/nchmemberseal/3876.png" alt="Click here to visit The National Council for Hypnotherapy" />
Copy it, paste it on a sidebar text widget (drag a new one or replace the old) and save it.