It has become the defining image of China's Tiananmen Square protests in 1989 - one man standing in the way of a column of tanks, a day after hundreds, possibly thousands, had been shot dead.

But 30 years on, the Chinese authorities continue to try to erase all memory of the time when they almost lost their grip on power.

To test the effectiveness of the censorship, the BBC's John Sudworth took to the streets of Beijing to find out how many people recognise Tank Man today.