Scale model decals
Decals have been used for decades on model planes and cars to provide fine detail. This level of detail is too hard to reproduce on small scale models. It cannot be done with paint, but it can be done with fine printing.
Of course models in the past were limited to what the manufacturer provided. You build the kit on the front of the bx from the parts provided inside, and you applied the details, occasionally choosing between two different options.
Today, with the advent of computer design, this has changed. We can design and build any model we wish, so long as we take the time to learn to use the programs and equipment.
3D printers allow us to build just about any small scale object. Sometime this mean making parts of a whole and assembling them. Sometimes this means the whole object being made by the printer.
We might have an object 3D printed by first scanning another object. Or we might design something via software and the print our original design.
But type of printing does not produce colour, it produces shapes. So we will probably have to paint the printed object, and then add fine details.
Scale model decals.
We can design what ever fine details we want using any number of computer programs, and then print the results with decal paper. This decal paper work as any printer paper would.
Decal printing and computer 3D modeling allow us to create, rather than just recreate, scale models of anything we can imagine. Think of the fine detail than can be added with printable decals.