The hidden picture plays little or no part in the solving process, as it may mislead. An error sometimes comes to the surface only after a while, when it is very difficult to correct the puzzle. If guessing is used, a single error can spread over the entire field and completely ruin the solution. Cells that can be determined by logic should be filled. Solvers often use a dot or a cross to mark cells they are certain are spaces. To solve a puzzle, one needs to determine which cells will be boxes and which will be empty. Nonograms have no theoretical limits on size, and are not restricted to square layouts. For example, a black four followed by a red two could mean four black boxes, some empty spaces, and two red boxes, or it could simply mean four black boxes followed immediately by two red ones. Two differently colored numbers may or may not have a space in between them.

If colored, the number clues are also colored to indicate the color of the squares. These puzzles are often black and white-describing a binary image-but they can also be colored. For example, a clue of '4 8 3' would mean there are sets of four, eight, and three filled squares, in that order, with at least one blank square between successive groups.

In this puzzle type, the numbers are a form of discrete tomography that measures how many unbroken lines of filled-in squares there are in any given row or column.

Nonograms, also known as Picross or Griddlers, are picture logic puzzles in which cells in a grid must be colored or left blank according to numbers at the side of the grid to reveal a hidden picture.

Classic Nonogram download