1. Create a new canvas (7x7pixels) <--and click for a transparent canvas!
2. Make a 1 pixel black line on the very left side and the top of the picture.
3. Then, Select all (CTRL-A) and go to EDIT>DEFINE PATTERN
4. Name it 'GRID' then click OK
5. Go to the canvas of your collage and select with the Lasso tool the area that you want the grid to be in (or you can just apply it to the whole image, rather than selecting a certain part)
6. Right Click, and select FILL
7. On the menu, click pattern, and choose the GRID pattern. select OK
8. Deselect
