This image was acquired from
wikimedia. It was marked as Public Domain or CC0 and is free to use. To verify, go to the source and check the information there.
Keywords from Image Description:
Crosshatching.svg An example of crosshatching in the solving of Sudoku puzzle Original puzzle layout by Lawrence Leonard Gilbert generated by the GNU program Su Doku Solver Cross hatch design by Adam Wood Both images released into public domain by their respective authors SVG version created in Inkscape Tim Stellmach Released into