Taken 50 years ago next month, Allan Milligan's powerful image of a razor blade-wielding thug slashing at a plain clothes policeman has achieved a level of notoriety almost without equal in the history of Scottish press photography.
Contained within a single frame is a story of sectarian tensions and bloody violence that would cause shock across the nation.
The date was October 16, 1971 and unrest was anticipated as a march organised by the Irish Solidarity Campaign, who were protesting Britain's military presence in Northern Ireland, got underway in Glasgow.
There were violent clashes as a group of loyalist counter-demonstrators arrived to meet the march at Renfield Street.
Among them was 17-year-old Brian Stewart, from Bridgeton, who slashed at 16-year-old James Cook, leaving him with a deep wound.
It was then that plain-clothed Detective Inspector George Johnston, cigarette still wedged in his mouth, pounced on Stewart and attempted arrest.
DI Johnston, however, got a little more than he bargained for as the teen thug again wielded his blade, slicing the experienced Special Branch officer on the face and arm.
Watching it all unfold just yards away was Kenny Black, then aged 14.
Up until that point, Mr Black, who is now 64, told Glasgow Live it had been just another Saturday up the town with his friend, Stuart Haughan.
Being young, he says he had been completely oblivious to the fact the politically-charged march was even on.
Mr Black said: "Basically, we couldnae believe what had just happened.
"The guy came out, jumped, and caught the detective's face and arm as he was going for his truncheon.
"Straight away other police officers were on him (Stewart) and arrested him. He was taken away quite quickly.
"The moment it happened we dived into a shop doorway to get out the road. We were no more than 70 yards away."
Mr Black, who was a schoolboy at the time of the incident, would later go on to serve in the police himself, spending 12 years in the force in his native Cumbernauld.
Reflecting on the events of October '71, Mr Black said he and others who witnessed the incident were left "disgusted" by it.
He added: "I remember it was fairly busy, and that when it happened the majority of people moved to the side. People were quite disgusted by what was going on.
"My reaction was more or less the same as everybody else's at the time - it was shocking."
Two months after the Renfield Street incident, on December 14, 1971, attacker Brian Stewart appeared at the High Court in Glasgow and sentenced to eight years at a young offender's institute.
During the trial, Stewart's defence claimed he had found the weapon he had wielded in Sauchiehall Street.
It was also claimed that because DI Johnston had been in plain clothes, Stewart had assumed he had been a member of the Irish demonstration.
