1 - Open the picture or graphic, or whatever it is that you would like to add a grid effect to. Open an new window ( Ctrl + N ) with the following properties:
Width: 10 pixels
Height: 10 pixels
2 - Select the first 1 pixel column and row of the graphic with the marquee selection tool. (as seen in below)
3 - Fill the selecton with the desired color, then deselect ( Ctrl + D ). Now select the entire image ( Ctrl + A ). In the menu, select Edit>Define Pattern Select the image you want to add the grid to, create a new layer, and go Edit>Fill , choose Pattern from the pull-down menu, click OK .
FINAL :
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Congrats B)
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