A grid of numbers hides a picture, paint the right cells so every clue matches the filled count around it, and the image emerges.
Mosaic is a pure-logic paint-by-deduction puzzle. Every numbered cell is a clue telling you exactly how many cells in its surrounding 3×3 block (the clue cell included) must be painted. Satisfy every clue at once and the board resolves into a hidden picture.
Work outward from the most constrained clues. A 0 means none of its nine cells are painted; a 9 means all of them are. Use those certainties to chip away at the numbers in between.
This puzzle type has no recorded inventor, which is common for forms that circulated through puzzle magazines before anyone thought to credit them. What it has is an obvious family.
Its two nearest relatives are the nonogram, which also resolves a grid of numeric clues into a picture, and Minesweeper, which uses the same 3×3 neighbourhood count as its only source of information. Mosaic takes the counting rule from one and the emerging image from the other.
The difference is that every clue here is local and complete. A number states exactly how many of the nine cells around it — itself included — are painted, so the whole grid is a system of overlapping small sums, and the picture is a by-product of solving them rather than something you are aiming at.
Mosaic is a neighbor-count logic puzzle in the paint-the-grid family, where deduction alone reveals a picture with no guessing required. This is an original, free browser version with daily and practice puzzles, playable instantly with no download or sign-up.