Step 1: Cropping width
When it comes to repeated pixel by pixel cropping, my editor of choice is MsPaint. Simple. When choosing a photo, the higher the resolution the better.
Load your image in to Paint. Ctrl + E will bring up the Attributes menu.
What ever your value is for width, divide it by four.
The first time, update the image properties window with the new value. The value shown below is that of my desktop. If I were going to do this, I would enter 320.
Paint updates the image attributes by extending or cutting off the right and bottom edges. To isolate a middle chunk, you need to re-open the original picture. Enter twice the previous value. My previous value was 320. This time around I would enter 640. This will set our new right boundary. After this, rotate the image 180 degrees so it presents upside-down. Bring up the Attributes window, and re-enter the original 320. This will cut the image to the correct width by cutting off the front. Rotate the image another 180 degrees, and save.
To get the third column, enter three times the original new width (my 320 would be 960) Rotate the image, cut it back to the needed 320, and rotate it up-side up.
For the final column, rotate the image, and just cut the width down to 320, and put it back.
If you saved each one of these as a new file, you should have four slivers of image.