1Two simple ideas
A picture is just light-or-dark squares — and ink stacks up
First we'll turn a picture into a tiny grid of squares: some dark, some light. Then the key trick: each square is printed as four little specks, and when you lay one sheet on another, ink blocks light — a speck that's dark on either sheet stays dark.
A picture = a grid
Every picture is just squares. Dark squares and light squares, lined up. Zoom in far enough and that's all a printed picture really is.
Ink stacks up
Each square = four specks, half of them inked. Lay two sheets together and the dark specks pile on top of each other. Lined up, a square stays half-gray; offset, it fills in solid black.
2The two-sheet trick
One sheet is gray fuzz. Two sheets are a picture.
We split the secret into share A and share B — two sheets of random specks. Here's the same secret, seen two ways:
Random gray fuzz. Every square is half-inked — no picture, no pattern, nothing to read.
The picture pops out! Stacked, the secret squares turn solid black while the rest stays light gray.
3Your turn — line up the sheets
Slide share B onto share A and watch the secret darken in
Drag the slider to lay share B on top of share A. While the sheets are offset it's all blotchy black. As they snap into line, the picture's squares stay solid black and the background fades to light gray — the hidden picture appears as that contrast.
Sheets offset — every square is blotchy black.
4Now try to crack it
A spy steals a sheet 🕵️
A spy gets their hands on your shares. The big question: with only one sheet, how much of your secret can they figure out?
Guess before you find out
The spy grabs exactly one of the two speckled sheets — half the pieces. How much of your secret picture can a clever spy work out from it?
The spy holds 1 share.