Stephen McGinty: The sinister side to horsing around is curiously appealing

WHY do I find the image of a man in black trousers, a purple jumper and a horse's head, standing silently on an Aberdeen street so disturbing?

To others, "Horseboy" as he is now known, is a figure of fun, an inventive comic jape – but I can't help but think of the murderer Michael Myers in the classic horror film Halloween. There is a scene where he stands beside a high hedge in a boiler suit, wearing a twisted rubber mask. (The director, John Carpenter, used a William Shatner mask.) In the next shot he is gone, the essence of evil vanished in a puff. Then there are the residents of Summerisle in The Wicker Man who taunt the hapless policeman, played by Edward Woodward, by standing in the streets wearing the heads of hare and deer and fish. The horror is not that they chase or pursue their prey, but stand and wait for him to come to them.

Or, in the case of Horseboy, for us to come to him.

I hope it is true and not a prank; that sometime last year a man in black trousers and purple jumper spotted the Google Street View car driving down Hardgate, near the junction of Riverside Terrace, pulled on his mask and waited while the camera car recorded his image. And that he waited knowing that sometime, in months or even years, his startling image would be revealed to an unsuspecting member of the public.

According to reports, it was one Russell Moffat, 50, who was using Google Street View to find an optician and stumbled on an image that made him question his vision. The symmetry of Mr Moffat's search has made people suspect that he indeed may be Horseboy, but apparently not. Since he mentioned his discovery on Twitter, Horseboy has become an internet hit.

I'd like to think that like hidden "easter eggs" on DVDs and computer games, there is a whole host of startling images of people standing, lying or sitting down in strange alleys and winding paths on Google Street View.

We have already seen the Norwegian scuba divers who chased the Google car with a harpoon gun, and the waving Paddington Bear on the streets of London. But perhaps my imagination is too dark, infected by multiple movies, because I wonder when the first "Google crime" will be uncovered. When will a member of the public click on a particular street and spot a stabbing in the corner of the frame, or the photograph of wasteland where a wall conceals all but a woman's kicking legs? Or a nondescript man in a crowded scene disposing of a weapon in a litterbin?

There is such power in a single frame – we see a startling image and cannot help but rewind or fastforward, and in the process fill the unknown with fantasy and fears. Thomas Harris created his novel Red Dragon about the serial killer Hannibal Lecter from a single image of a calm man sitting in a cell.

Some pictures, like the CCTV footage of the killers of James Bulger leading the little boy to his fate, are powerful for what we do know. Others, such as that of a worried mother with her children, shot during the Great Depression, are powerful for what we don't know. Even dramas recognise the power of a single photograph – think of Deckard in Blade Runner or Timothy Spall in Stephen Poliakoff's Shooting The Past, tracing the fate of a Jewish girl in Nazi Germany through a handful of photographs. The still photograph has an amazing ability to make us stop and think about the present. For me, Horseboy is a meditation on perpetual surveillance and the secret of the past.