A few years ago, I became fascinated with Three dimensional (3D) modeling applications that allow you to create objects to be viewable from any direction. This lets you reuse an object (boat, person, tree) more than once, since you can later alter the appearance of an object to fit your needs. Of course,the time required to create 3D object in the first place is not trivial and represents a large time commitment.
Once created from polygons mathematically, the objects can be combined in various ways, or new ones can be created on the fly.
You can apply textures and materials to 3D objects to create completely different ones. For example, a mountain can become a purple mountain in the distance, or a grassy field up close. In addition, atmospheres can change the lighting and determine where shadows fall.
Some digital artists do not use 3D objects, but instead paint using a computers' mouse or graphic tablet and stylus with photo editing and draw programs to create the art. Many of these artists primarily create abstract paintings or perhaps edit photographs they have taken with a digital camera.
As you can see from my work, I don't use either of these techniques, but rather produce representational artwork that comes from my imagination. Usually none of my work starts as aphotograph.