Dragos said:
Where the designer's rights ends and where the user's rights starts?
I think this is the big question.
The rights of the designer (as copyright holder) and the user depends on what copyright laws you are under.
I am not a lawyer. So my opinion won't cost the US $200 to US $400/hour that copyright lawyers charge here in the United States. However, I have had to do some research into U.S. and international copyright law recently and may be able to provide some useful information.
In the United States, when you by a copyrighted item, you are actually buying a licensed
copy of the original work. The license gives you a set of limited rights to use the copy. It doesnot convey unlimited use rights to the copy and it certainly doesnot give you the right to make unlimited additional copies of the copy without permission of the copyright holder.
Other parts of the law give artists certain use rights over original art pieces no matter how many times they are sold or resold. The law also has a "fair use" provision so that
limited portions of a copyrighted work can be quoted for journalistic or scholarly research purposes without first obtaining copyright holder permission. However, republication without permission of a copy of an entire work (or paper model), even if it was made available for free download, would exceed reasonable "fair use. "
As for commercial works, if any part of a copyrighted original design appears in your model, your model is a "derivative" work and you must have permission of the original copyright holder to use
their parts in your model. It doesn't matter how much or how little of their design is in your model, if you make it a different size, or if you make cosmetic changes to their design. If it is recognizeable as the original copyright holder's design, then you have to get permission.
However, as the author of a derivative work, you do have original copyright on anything that you added to the original model design. For example, if your derivative model is 10% someone else's design, you are the original copyright holder on the 90% of it that is your original work. (This would be important if someone in the future tried to use your model without permission.)
There are a lot of older Eastern European paper model kits on the market.
If I understand the international copyright law I read correctly, just about everything published in the old Warsaw Pact or Soviet Union prior to it's dissolution in 1989 is considered to be in the public domain (copyright free). Publishers may regain some copyright control over pre-1989 works by subsequently reissuing the item under copyright after 1989. However, under U.S. copyright law, this republication would probably be considered a derivative work and the publisher would only have copyright on any new additions made to it. The underlying original would still remain copyright free. Of course, anything issued after 1989 in Eastern Europe or Russia is covered by applicable national and international copyright laws.