Two clarifications:

1. If you intend to publish [reproduce the image] for sale then registration with the Copyright Office is suggested. Why? In the event of legal proceedings, the completed Copyright registration is the "Proof" you "own" the image in question. While you don't have to register it is a safeguard that may protect your profits.

2. Most of the Poser / 3d Modelists sell their work on the basis that your payment is purchasing a "license" to use their work [3d model] in the manner set forth in the license provided with the model / morph.

Using a model that you have not paid for or using it in a manner that violates the model maker's license will put you inviolation of their copyright. So always be sure of the source of the works you are using and that the model maker's license allows you to use it.