photoshop – Black/White Checkered Graphic

Create a new doc the exact number of pixels across and down as the number of squares in the graphic you want.

Zoom in on the new canvas

Use the pencil tool, set it to 1 pixel in size and create the squares in their approx location – at this size the pencil will look like a square.

Once done, resample your image (Image -> Image Size) to the size you want it to be – with Constrain Proportions checked and the interpolation method as Nearest Neighbor.