"Passers-by on a London street were recently amazed to see a fleeting image of a pink tongue protruding from fruitily plump lips, seemingly suspended in mid-air.
It was the famous logo for the Rolling Stones and was part of an experiment by tech start-up Lightvert.
Its technology can produce images that appear to be 200m (656ft) high, but which only exist in the eye of the viewer for a fraction of a second.
So could we be on the verge of seeing giant digital ads in our cities, similar to those featured in the seminal 1982 sci-fi film Blade Runner?
Lightvert certainly hopes so.
Its tech, called Echo, works by employing a narrow - no more than 200mm - strip of reflective material fixed to the side of a building. A high-power projector mounted below or above the strip beams light off the reflector directly into the viewer's eye.
The image appears momentarily, exploiting what's called the "persistence of vision" effect - the way sparklers seem to leave a trail of light when you wave them around quickly."