This picture came about quite by chance. I had taken the picture from Hungerford Bridge on a misty morning, and the whole scene was in pale shades of gray. I decided to increase the contrast just a little; but, as sometimes happens, the slider had a will of its own and slid right up to maximum. I liked the effect, so I saved it.
I used this picture once before, in the banner for the London Algebra Colloquium site on WordPress.