You can clearly see a circle on the screen, but nothing can be seen on a screenshot taken of it. In the interesting game MOTUS, a familiar expectation is turned on its head: what you see on the screen should also be able to be captured as an image, but that fails here. The trick is not a recording lock. The shape here is not in the pixels themselves, but in how pixels change over time. A single frame does not capture these changes.
The developer Branta Games makes the source code freely available in GDScript, a programming language developed specifically for the Godot Engine. This cool effect occurs because our vision also evaluates changes over time. The brain combines points that move together into an area; so the circle stands out from the stationary background. A single image, on the other hand, only shows similarly distributed gray values, but neither direction nor speed.
See the Pen Der unmögliche Screenshot – ein Kreis im Rauschen (WP5364) by David Vielhuber (@vielhuber) on CodePen.
In the game, several areas differ in speed: At \(60\) frames per second, a shift in every second frame means \(60:2=30\) shifts per second. A distinction must be made from the Pulfrich phenomenon : if you only darken one eye and keep both eyes open, it processes the movement a little later. The brain interprets the resulting image offset as spatial depth. However, you do not need this additional effect to recognize the circle.
So a screenshot can easily save the points, but not their movement. A video recording, on the other hand, preserves the successive images and thus the crucial indication of the form. Technical evaluation of several individual images also remains possible; The effect is therefore not copy protection. The supposedly impossible screenshot is, above all, a clear example of how our vision not only evaluates brightness and colors, but also changes over time.