![](https://blogs.sas.com/content/operations/files/2015/12/grid-shading-puzzle-lowres.jpg)
The British spy agency GCHQ recently posted a grid-shading puzzle that the director sent out in his Christmas cards this year. The puzzle, shown here, is known as a nonogram and by various other names, including Paint by Numbers and FigurePic: Each cell is to be colored black or white,