How can tilting a card reveal a different picture?

Some picture cards seem to change their drawing when tilted, without a screen or battery. A smooth-looking plastic cover actually contains rows of tiny parallel cylindrical lenses. This kind of image is called a lenticular print. Light and careful alignment do the selecting.

Two pictures are first divided into narrow strips. A strip from picture A lies beside a strip from picture B, and this pair repeats across the print. Each little lens covers one pair. The strip spacing must match the lens spacing; simply putting an ordinary full picture under the plastic would not produce the intended switch.

Each curved lens bends light from different positions beneath it toward different directions. From one viewing direction, light reaching the eye mainly comes from the A strips across many lenses. The eye receives their separated pieces as picture A. From another direction, the B strips become visible instead. Tilting changes which direction the viewer has relative to the card.

The main drawing shows both routes together, with four repeated lens cells selecting matching strips. It is a schematic two-view design, not a measured lens prescription. Real cards can briefly mix images between intended viewing zones, and poor alignment can cause persistent overlap. More views can suggest motion, while carefully chosen views for two eyes can suggest depth. Neither effect requires the plastic to store a hologram: a lenticular print redirects light from ordinary interlaced images.