Make a pattern
1. Open a new document, high resolution, size about 2 inchesx2 inches, transparent background
2. Select>All
3. Edit>Stroke. Choose white, check the Inside box, about 10-20 pixels to your taste
4. Edit>Define Pattern
5. Open your photo, make a duplicate or put it onto your layout.
6. Go to Layer>New Fill>Pattern
7. In the drop down box, your grid will be the last pattern in the list
8. Scale/Resize as desired
9. Layer>Layer Style>Drop Shadow to make the grid look on top, or Inner Shadow to make the photo squares look on top.
10. You have to save your grid as a .pat file or it'll be lost if you ever view other patterns. Go to Edit>Preset Manager, choose Patterns, select the grid, then Save and name the file. To add anything to it later on, just Load and select all the patterns you want to include and save over the pat file. One I like is to rotate the original image 45 degrees for a diamond grid and save that as a pattern and save with my other grid patterns in a grid.pat file. I have circles, squares, diamonds, other colors, be creative
