Following the robbery of a £50,000 watch, detectives in Kensington and Chelsea are releasing the images of two men.
The incident happened on Thursday, 3 May at about 18:20hrs on Franklins Row, SW3.
The victim, a man in his late 20s, was walking his six month-old Mastiff puppy. As he did so, he was approached by two men.
Suspect one grabbed the victim by the shoulder, while suspect two produced a knife and held it to the victim's stomach.
They demanded he hand over his Audermars Piguet wristwatch, which has rose gold links and is valued at around £50,000.
The suspects then made off towards Turks Row.
The victim was not injured, but was left badly shaken.
Both suspects are described as white, aged 25 to 30 and suspect two spoke with a London accent.
Detective Constable John Fellows said: "These men used a knife to threaten and rob a man in broad daylight. They are clearly dangerous and we urgently want to identify and locate them.
"We are appealing for anyone who recognises these men to contact police immediately or contact Crimestoppers anonymously if you don't want to give your name.
"We are also asking for anyone who saw the incident or saw these men hanging around the area to contact us. Your information could be vital in helping us find these men."
Any witnesses or anyone with any information is asked to call police on 101 or tweet @MetCC. Quote CAD 6263/3May.
To give information anonymously contact Crimestoppers on 0800 555 111 or online at crimestoppers-uk.org.