Julius von Bismarck's 'Image Fulgurator' projects stealth images into the photographs of strangers, while keeping those images invisible to human eyes. Depending on whom you ask, it's either a clever hack or an obnoxious intrusion. Naturally, we had to find out more.

Yesterday, von Bismarck's device made its premature debut on the internet. Today we met him in his hometown, Berlin, to talk about the device, the thinking behind it and the inevitable deluge of e-mails from viral marketers wanting use it to smash their way further into our brains.

But first, about that name: According to von Bismarck, 'Image Fulgurator' comes from the Latin for 'lightning' (fulgur) and means 'Flash Thrower'.

First, let us make clear that von Bismarck has applied for a patent for the Fulgurator. He stressed this point. Of course, anyone with the requisite skills can make one of their own, but Julius wants to keep some degree of control over commercial use.

To see why, consider how it works. The device is a modified camera – in this case, an old manual Minolta SLR. A flashgun fires through the camera in reverse, from the back. The flash picks up the image of a slide inside and projects it out through the lens and onto any surface.

The trick is in the triggering. The Fulgurator lies in wait until an unsuspecting photographer takes a picture using a flash. When the device's sensor sees this flash, it fires its own unit, throwing up an image which is captured by the hapless photographer's camera while remaining unseen by the naked eye.

Now, imagine for a moment that an ad agency gets hold of this. You couldn't take a photograph of a tourist attraction ever again without worrying that some marketing crap would be pushed into your camera. As Julius told me, "I see it as a piece of media art. It could be a dangerous attack on media. [But] if people do shit with it, I feel bad."

This is the reason for the patent, and although he doesn't have an army of lawyers behind him, Julius seems to be on top of the legal side of things. He's also moving fast. This Fulgurator is the first prototype, and the most primitive. "It works, but it's not practical," he says. "In a few years time, huge companies will use it for shit," but by then, Julius will be at the next stage. He already has more working models (which I wasn't allowed to see) which are refinements of this one.

At its simplest, the Fulgurator is a very easy hack. A hole has been cut in the back of the camera and a piece of clear, roughened acrylic put in its place. A rear tube allows the flashgun to slide in. Everything else remains intact. The slides themselves are just rolls of processed film (the pictures are snapped from Julius' computer monitor) returned to their canisters and then loaded up as if a normal film. Any image on the reel can be selected by turning the rewind crank. When you hold the Fulgurator up, you can see the subject on the acrylic screen and line it with the image on the slide. You can also focus, to ensure the final projection ends up sharp.

But the magic happens inside the flash sensor on the top. Ordinary slave flashes (which fire whenever they detect another flash going off) aren't reliable enough, so von Bismarck built his own circuitry. The original was based on the Arduino platform but has evolved into a custom-made circuit. The knobs were for tweaking the settings on the prototype, stuff which is all now taken care of by software.

Julius had ripped the guts out of the box for a newer version, so we couldn't see it in action, but we know what it does. Modern digicams flash for all kinds of reasons, such as red-eye reduction and focus assistance. What Julius' circuit does is to ignore all of these false strobes and fire only when the photo itself is taken. This is the secret sauce of the Fulgurator.

Clearly, this is a prankster's dream. But Julius thinks it has a serious side, too, which is why it looks like a gun. "It's important that people know it's not just a funny idea," he told me, "it can also do negative stuff."

It seems that the "negative stuff" consists mainly of pissing people off, like the aforementioned marketing uses. We're looking forward to seeing what the next gen hardware can do, though. Take a look at this picture:

The message is 'Fulgurated' onto a black laptop bag. Turning black to white is powerful stuff, but it's not just slogans that can be fired. Although Julius frames his nerdery in an artistic context (he's studying a German Diploma called "Digital Class" at UDK, Berlin's art school) he clearly has a soft spot for tomfoolery. In the image below, you see an image of a naked body which can be projected onto a clothed person.

The possibilities are endless, but Julius is just getting started. When I suggested that he put his own URL on the images, so victims could later check to see just what had happened to their pictures, he seemed surprised (later I learned that he does plan to include it later, to promote his own work). In fact, the whole thing has happened a little too quickly.

Yesterday's 'leak' onto the internet was intended as a place holder for an entry into Ars Electronica's Cyber Arts exhibition in September. Instead, it catapulted him into internet fame and he has already received high-priced offers for his work. If he manages to keep on top of things, this little hack could make him some big money.

Image Fulgurator [Julius von Bismarck]