Your image is likely 3x2 in aspect ratio.
Using the Crop Tool create a ratio that is 1x2
Place the Crop on the Left side of the image and crop and export.
Recrop choosing the Center of the image and export a second file
Recrop again choosing the Right side of the image and export a third file.
When you set three exported files size by side it should look like your example. Send the three files in and get three prints made. Then it is up to you to hang them all level!
thank you Rikk for your reply. I've had a go at it but am having difficulty since my images are almost always cropped first (so therefore no longer in a 3x2 aspect ratio). if for example i cropped the image to an 11x14 ratio before doing this, what would you suggest? Perhaps I could make three 11x14 images out of the one 11x14?
also, i'm wondering when you write "recrop choosing the center of the image" are you doing this by sight based on where the previously cropped and exported left side image ended (on the right side of it), or is there another way?
Thanks again for your help.
For an 11x14 (assuming the 14 is the horizontal) set your crop ratio to be 4.8x11 and use the steps I put in my original answer. .
Thanks again Rikk. I will give it a try. I am assuming though you meant 4.7 (i'm assuming you've divided the horizontal here by the number of panels).