Effect of Radial Distortion
Explanation: Black dots should form a rectangular grid. However, if the camera lens has radial distortion, image will be distorted. This animation simulates the photo under different radial distortion parameters. More specifically, the distorted image point is given by $p \mapsto L(r)\times p$, where $L(r) = 1+k_1\times r$, and $r = \|p-c\|$.