4 the modelling of caustics to produce a projection image

The Projection-Based Image is a new banknote security feature that projects a desired image when an array of microlenses embossed into the banknote substrate is exposed to a light source. The feature is designed computationally to make the projected image difficult to discern by inspection of the lens structures, and to accommodate a range of light sources, allowing wide accessibility to users with a simple mobile phone flash. The projected image is formed from a collection of Gaussian-shaped caustic profiles, each arising due to light refracting through a single microlens.