Look closely and you can find digital graffiti — videos, animations, and comments superimposed on buildings and streets around the world.

They are created using apps for smartphones or tablets to edit augmented reality (AR) YouTube videos, New Scientist reports.

Most major cities are teeming with these digital annotations. You just need to identify a tagged location using your smartphone’s map, and watch through the camera using an AR app.

Now Tobias Langlotz of Graz University of Technology, Austria, and colleagues have designed software that can cut a person or an object out of their own video, so they can be pasted as a digital overlay. The idea is to make virtual human guides that could offer city tours or how-to demos, as well as enhancing AR games.

Langlotz and colleagues used a computer-imaging technique called foreground-background segmentation to identify the required foreground object, usually a person. So a user would film a video, then simply point to the object they wanted to extract. The software would do the rest.

In a demo, they filmed a skateboarder doing a jump, and showed how he could be pasted onto a street scene. When the app “sees” the environment, it can replay the person in the right place, skating along the ground, for example.