Photo Montage (the Nudge Method)
I would normally recommend that you use another method.... but this one seems to be the easiest way to do this. If you have Photoshop you should read the Center, Align, Distribute Trick.

1. Crop your images. You can assign a pre-set size and resolution to the Crop Tool in Photoshop.

2. Import all of your images in Photoshop. If you copy/paste them they should all be centered. Holding the "shift" key while dragging an image, will center it on the new one.

3. Link the images that will create your top line.

4. Select the Move Tool (V) and nudge the linked images to the top: count how many times you've moved them up(13 in this example.

QUICK TIPS

• You can hold the CTRL key instead of selecting the Move Tool...
• Holding the Shift key will nudge layers by 10 pixels at a time.
• Holding the ALT key will make a duplicate of your layer.

5. Unlink the images.

6. Move one to the left (remember to count).

7. Unlink the images.

8. Move one image to the left (remember to count).

9. Move one image to the right (remember to count).

10. Repeat for the remaining rows.

Voilà!