The journalist Shiv Malik took a rather intriguing photo at the recent student protests.
It appears to show a group of police officers gathered around a blue box. No one seems to know what the box is for. I'm sure it's got a rather prosaic function - but that doesn't stop the speculation!
As soon I saw it, I could think of only one thing; chroma-key! (Or Colour Separation Overlay if you're the BBC). It's more commonly known as "blue screen". It's the special effect which allows you to remove the background and replace it with something else.
So, using my rather unimpressive GiMP skills, I created this version of the image with the blue box removed.
Mike Stead created this quick image.
And I produced this (rather obvious) effort.