First lets create the square pattern. Open up a new document 7x7 Pixels with a Transparent background. Then zoom in all the way so you can actually see what your doing.

Reset your colors then grab the Pencil Tool with a 1 pixel diameter and draw a box like below ensuring you leave a 1 pixel border around it.

Now let us define the pattern. Go to Edit--> Define--> Pattern type "Squarilate" and then hit the OK button. You can close this square pattern window now.

Open the image you want to add this square background on or use the image we provided below. The image is really big so you can see the full effect of this square background.

Once you got that open, create a New Layer then go to Edit--> Fill. Under Contents and the "Use:" dropdown menu select Pattern then under "Custom Pattern" find the square pattern you just made. Choose Normal for the blending mode and have the opacity at 100%.

Now change the Blending Mode to Overlay and set the opacity at a low percentage(20%).

To further enhance this effect grab the Eraser Tool and have it at a soft 200 pixel brush size.



Then go over the main parts of your image, it maybe a person, object, or whataever. In this case it's the abstract art and we want to put the focus on the brushing and such so with the eraser tool go over the abstract parts deleting the square pattern background.