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An image of a Playboy centrefold has been shrunk down to the width of a human hair by scientists in Singapore.

A team from the Agency for Science, Technology and Research (A*STAR) printed a colour photo, measuring just 50 micrometres across.

The photo is a crop of the portrait of Lena Soderberg, a Swedish model, that originally appeared in a 1972 issue of Playboy.

It is a commonly-used image for testing printing techniques.

In the journal Nature Nanotechnology, the researchers stated that the device could produce colour images of up to 100,000 dots per inch - 10 times as many as a high-end home printer.

The method could be used to print tiny watermarks or secret messages for security purposes, said the scientists.

"Our colour-mapping strategy produces images with both sharp colour changes and fine tonal variations, is amenable to large-volume colour printing… and could be useful in making micro-images for security," in its research paper.

According to Chad Mirkin, a nanotechnology professor from Chicago's Northwestern University who was not involved in the study, the result is "approaching the limit of what is possible to print in colour".

If the pixels were brought any closer, light reflecting off them would diffract, causing the two objects to blur together.

To obtain the image, the team used tiny silver and gold particles, which, when arranged in a certain manner, produced colour.

"This is a clever way of creating desired colours," said Prof Mirkin.

"Instead of taking normal dyes and using conventional printing, they're making colours out of one material by adjusting nanostructure in a lithographic [a technique to create patterns] experiment.

"They're getting these high-resolution images in a context of colour, and getting the colour in a way different from dyes that make up clothing or pigments in paint."

He stressed that it was not, however, an advance in high-resolution printing, as there were other techniques that were substantially superior.

For instance, scientists at the University of Nottingham created a microscopic portrait of the Queen to mark the Diamond Jubilee that was so small it could fit on a standard postage stamp 300,000 times.

Ms Soderberg's picture was first used as a test image in 1973.

An assistant professor of electrical engineering at the University of Southern California Signal and Image Processing Institute Alexander Sawchuk was looking around his lab for an image to scan for a colleague's conference paper.

He wanted a different picture from his team's usual test images, and when someone came in with a recent issue of Playboy, he used the centrefold.

The scan became one of the most used images in computer history, and the model became dubbed the "first lady of the internet".