It can be either homemade or it can be commercially produced. Whichever method is used, the market is very secretive. Homemade material often involves neighbourhood kids who are manipulated and bribed, not fully realizing what they are doing. Much of this material is not distributed. It may be swapped with other pedophiles, but quite often it is merely for the owner's own use.
Photographs are the most popular medium.
This is likely because they are relatively easy to produce. They are often done by those people who are sexually abusing children. The Badgely Report expressed concern over the use of videotapes because of the ease of which they can be copied. The homemade material is probably the most common type of child pornography. Commercial material often involves runaway children who are older and need money to survive.