How can you just take pictures?

Use B-door exposure for a long time in dark environment. At the same time, ask your partner to wave words or graphics with a flashlight or any point light source in the camera's field of vision. Of course, if you are sure, you can also take a selfie with a tripod. But there are certain requirements for the user, that is, they must be able to draw.

In fact, this kind of photo is most obvious in the all-black environment, and the person waving it is also the most hidden. Because people are much faster than door B and are not fully exposed, they will be very unclear or even invisible in the photos.