art & text © by Rueben Bolling
The reason the constitution gives for copyright laws is to encourage the development of new ideas and discoveries that the public will be able to use for free.
"the Congress shall have power . . . to promote the progress of science and useful arts, by securing for limited times to authors and inventors the exclusive right to their respective writings and discoveries."
To fund this, the original innovators and discoverers were to be granted a limited time license in which they could have exclusive control over the innovation / discovery, after which it was to enter the public domain.
The idea was that after a reasonable period said creations and discoveries would be available for everyone to use freely without permission or cost. While the original period of copyright was fairly short, for most of the 20th century it was a total of 56 years in the US. Now it's 95 years (works for hire) or lifetime of the creator + 70 years.
Disney and others have extended copyright to a grotesquely long period. Maybe the original max of 56 years was too short but 95 years for works-for-hire and life of creator + 70 years are much too long.
Let's use the Mouse as an example. His official debut was in 1928, meaning by the terms of copyright in that era he should have entered the public domain in 1984.
What Disney has done has been to reissue old material with small but distinct changes or additions, thus making them "new" creations under copyright, and by trademarking every single iteration of the Mouse they've ever done.
The way the system was originally designed to work, at this point Disney would be able to keep issuing new Mouse product and advertise same as the only genuine or official Mouse products, but other people who had ideas on what to do with the Mouse were free to do so.
Frankenstein, Dracula, Jekyll & Hyde, Sherlock Holmes are all public domain now; anybody can use those characters.
The argument against extended copyright is that if an entity owns a stable of properties, they have no incentive to create new product, simply do countless reiterations of the old. A few years ago Paramount re-released the original Star Trek series with new CGI effects to replace older film opticals; this was done to extend the copyright on those episodes for another 95 years.
And as most major media entities have larger war chests and longer reaches than citizen creators, they can effectively squeeze new properties out of the market place.
Disney's movies based on public domain works are trademarked re the specific look and design of the characters. There are copious imitations and knock-offs out there, but they have to be careful to steer clear of Disney's specific designs.
Methinks the average customer can tell the difference between these versions of the same story.
And certainly this one!
There is an ill-defined area called "fair usage" which includes parody but the specifics of what parody consists of are even more ill-defined. Roy Lichtenstein escaped plagiarism lawsuits leveled by creators and small publishers he ripped off, but he did one painting of Donald Duck and Disney threatened to drag him through every court on the eastern seaboard if he ever did it again so he didn't.
Now, either Lichtenstein was wrong in the first place and he did rip off creators and companies, or Disney was wrong to threaten him, but they both can't be right and from where I sit it seems that the more money you have (and Lichtenstein was wealthy for a fine artist tho nowhere near Disney wealthy) the more you can game the system for your own advantage.
 Meaning Keith Richard's music may not enter the public domain until the 22nd century if his health holds out for another 13 years!
 Irving Berlin lived long enough to see his earliest songs go into the public domain and neither he nor his heirs seemed to have missed any meals because of it.
 Many of the earliest comic strips are public domain, but Disney won't let anyone use the name Mickey Mouse to identify them, so they're collected as "Classic Mouse Comic Strips".
 Trademarks a.k.a. service marks are considered business brands and not creative works; they were originally limited to titles and specific logo designs, not characters, vehicles, etc.
 Tarzan is public domain, but ERB trademarked the image of Tarzan as a beardless white guy in a loin cloth so if you want to do that version of the character you have to pay ERB Inc. It's theoretically possible to do Tarzan as a bearded guy of mixed ancestry in jungle fatigues but probably not worth the risk from ERB Inc's lawyers. And if you want a really complicated set of rights, take a gander at the confusion surrounding King Kong. There are at least four separate sets of rights involved with a number of other rights now in the public domain including the original novelization.
 The internet was supposed to democratize access to the public, and in one sense it has, but it's difficult for private citizens to monetize.