Mister Butterworth, late of her Majesty's Royal Navy, in the photograph on the mantlepiece at Mrs Butterworth's left elbow.
Also It looks like the Prisoner is having a quick measure up, to see if the measurements check out with the size of room he once knew! Well why not, he remembered the damp patch behind the bureau which was made good. The opening of the bathroom door, sliding to the left, and the hot and cold taps of the shower, which had been put on the wrong way round, so why not take measurements so as to have conclusive proof?
Mind you having said that Mrs Butterworth does look rather put out by No.6's antics!
Be seeing you