I know this is still gray territory and it is asked so many times within the 3D printing and maker community but I'm curious about the limits of 3D models and were it touches on Free Use and infringement. I'm not trying to push the envelope, I just want to be clear on the matter.
Is it legal if a design is rendered in a CAD program of a copyrighted material for no purpose of using, distributing, creating, mixing, internalizing, re-licensing under GPL/CC, or any unauthorized use outlined by the owner of the original work? For instance, if someone is demonstrating the abilities of a particular CAD and makes a mock-up of Mickey Mouse just to show the limits of said CAD and the STL/OBJ isn't released or distributed and a letter of intent is given along with the demonstration regarding the original work (in this case, Mickey), is that infringement? In this example, no loss of revenue or sales will affect the original owner, no claims of ownership is implied or stated, and no physical model will be created.
While considering all of this, I figured that it wasn't very much different than if an artist sat down and drew a picture of Mickey Mouse. As long as the picture isn't sold, distributed, or released, in my mind, that is the same thing as a 3D render.
To further the details of the 3D model, the render would be made from scratch and not imported, copied, or reverse engineered from any other work. Bottom line, it will be a likeness that is created but it will be as close to the real thing as possible to demonstrate capabilities of a particular program (such as organic shapes, stitching, grouping, layering, or any other facet and characterization of 3D modeling).
I already understand that it is recommended to err on the side of caution and steer clear of things like this but it is more of a curiosity than a request for legal advice regarding a specific case.
Can this be covered under Fair Use?
Since there is nothing to be made from creating the render, it isn't released or distributed to others, isn't re-licensed, and no ownership is implied/credit to the original owner is given, is this Free Use or copyright infringement?
Whether or not you sell, distribute, release, license, profit from, claim ownership, etc... of something does not matter for copyright law. Copyright prohibits the very act of well, copying. Specifically, if a work is protected by copyright, you can't (among other things)
make adaptations and arrangements of the work
make reproductions in any manner or form
without permission (or a license) from the copyright holder. Just because you do something privately, don't distribute or profit from it, does not make you exempt from this rule.
In some cases though, a fair use exception may apply. In the United States, uses that may be (but not necessarily are) fair are limited to:
criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research
Note that in Europe, teaching is usually not considered fair use.
So no, it would not in general be permitted to make a 3D model of a copyrighted work, even if you don't plan to do any of the things you listed with it. An artist would not be allowed to draw the picture of Mickey Mouse as you describe either. However, in the United States, your use could be construed as fair use for educational purposes. However, considering that you could equally as well have used some non-copyrighted work to demonstrate the limits of CAD (there's nothing specific to Mickey Mouse that makes him more suitable than any other model) I would recommend against this. An important argument in fair use is usually that there is no other option but to use the copyrighted work (e.g. in a class discussing pop music you have no option but to use excerpts of copyrighted lyrics).