This technique is suitable for small to medium sized boxes. It becomes cumbersome for dealing with large boxes because of the relatively large surface areas. It can be used by inventors to make their own custom product packaging to present a more finished product for licensing or to sell small initial quantities. It can also be used by someone selling hand crafted items and wanting to add unique packaging. Finally this technique can be used to make custom packaging for special gifts for that special someone you want to impress with your skill, thoughtfulness or how much free time you have to make custom packaging. The technique, although not taking a whole lot of time, is labor intensive and therefore usually limited to small quantities.
The first step for custom packaging is to find or make a template. A template can be most easily found from an existing box design such as custom retail packaging or a shipping box. You could even design your own. By ungluing the seams of an existing box you will see that the box will unfold to a flat sheet of cardboard that is printed only on one side. It is fairly easy to modify an existing design or come up with one of your own.
The next step is to transfer the outline of the box to image processing software such as PhotoShop. There are several ways to do this. One way is to take an image using a digital camera being careful not to distort the image by taking it at an angle. Try to take the image straight on. Another way to transfer the outline is to use a CAD program to recreate the outline. In either case you may want to store the original outline in case you have to go back to it after reconsidering a modification.
Scale the transferred package outline to the size suitable for your packaging. You can either scale the whole image or just alter a dimension or two such as height or width. In either case the outline becomes the cardboard boundary of your box. Mark the fold lines on the image outline by using registration points, usually a circle with an X or plus sign in the middle, outside the boundaries of the box outline. You will need these later to make the fold lines. You can make the registration symbols using the image processing or CAD software or simply use an X to mark the spot. It is optional to mark the fold lines on the image itself. I would recommend that if this is done that the fold lines are put on another layer so that they can be turned off if needed.