Public Address System - anyone know how to change my picture?

On the fine Russell Brown hosted (as in host of the dinner evening not this new fandangle web "host" we call talk about) Public Address System* I can edit my details (name, URL) but I'm danged if I can find how to change my picture.

Leave a comment and let me know how

* which I've just noticed is still "beta" - hee hee, nice one ... but then again so am I AND this blog