The 4xD print is a size that is compatible with the image ratio of many digital cameras that use a 4:3 ratio or 4/3 = 1.33

The 4xD is 4 inches by 5.33 inches.  Dividing 5.33 / 4 = 1.33.

Since a 4xD print has the same ratio as many cameras, no cropping is necessary for photos taken with those cameras. You will always see the complete photo when you print to a 4xD any photo taken by a digital camera that has a 4:3 capture ratio.