GIMP:
File > New > input pixel size of the image you want to do this effect on > OK
Filters > Render > Pattern > Grid
Your width & spacing will depend totally on the size of the image!
Colors > Invert
Layers > Transparency > Color to Alpha
If the color bar between "From" and "to alpha" is not white, click on the bar and set the V slider all the way to the right. Click OK
One more OK to make the grid
File > Open as Layers > load image you want effect on.
Layer > Stack > Reverse Layer Order
File > Save As... > create a new filename > choose image format (usually jpeg) > Export > Save.