The human visual system is particularly good at detecting small misalignments (ie as small as the width of a pencil viewed at 300m).
Today’s invention makes use of that fact to help provide screen displays which are less susceptible to ‘shoulder surfing.’
Such tiny misalignments in gratings of lines can be seen, but only when viewed from straight ahead. A shape can thus be seen in the diagram, formed simply by small jumps in the black lines. These jumps, and the shape, would be much less visible to anyone observing them from, in this case, the 10 or 4 o’clock position.
The display on eg an ATM touchscreen could flash up an array of apparent numbers formed from misalignments in a grating and a bank customer could then choose their pin number, without showing these digits to bystanders.