Most rights can be voluntarily abandoned ("waived") by the owner of the rights. Legislators can go to extra effort to create rights that can't be abandoned, but usually they don't do this.
In particular, you can voluntarily abandon your United States copyrights:
It is well settled that rights gained under the Copyright Act may be abandoned. But abandonment of a right must be manifested by some overt act indicating an intention to abandon that right. See Hampton v. Paramount Pictures Corp., 279 F.2d 100, 104 (9th Cir. 1960).
Micro-Star v. Formgen Inc., 154 F.3d 1107 (9th Cir. 1998).
Note for people not familiar with legal citations: After a "District Court" makes its decision in a United States court case, the losing party can appeal to the "Circuit Court of Appeals" that supervises the district court. These "Circuit Courts of Appeals" are run by about 200 of the nation's most experienced judges. Each appeal is heard by three of these appellate judges. My quote is from the unanimous decision of the three judges who heard the Micro-Star v. Formgen appeal.
For software packages using the SPDX format to declare copyright information, you can copy and paste the following:
SPDX-License-Identifier: LicenseRef-PD-hp OR CC0-1.0 OR 0BSD OR MIT-0 OR MIT
Here LicenseRef-PD-hp says "This work is hereby placed into the public domain". The remaining authorizations are redundant but help pacify various license-tracking systems: for example, at the time of this writing, FreeBSD requires special approvals except for BSD-2-Clause, BSD-3-Clause, ISC, and MIT.
Yes. You can voluntarily abandon your European copyrights. You can't abandon certain reputation rights (such as the right to stop people from removing your name from your work), but you can abandon your copyrights. See, for example, https://intellectual-property-helpdesk.ec.europa.eu/news-events/news/public-domain-2020-11-19_en:
The Public Domain covers the following categories of material: ... 4. The copyright owner deliberately placed it in the public domain. If, upon viewing a work, you see words such as, “This work is dedicated to the public domain,” then it is free for you to use.
(Boldface in original.)
Many Germans incorrectly believe that copyrights cannot be abandoned. The actual situation in German law is as follows:
Beware that many sources (including Google Translate) mistranslate "Urheberrecht" as "copyright". This error contributes to the common confusion among Germans on this topic.
Section 29(1) of the German copyright law says that, except for inheritance, "Das Urheberrecht ist nicht übertragbar" [the originator right is not transferable]. Mistranslating "Urheberrecht" as "copyright" would say that copyright is not transferable; but this is contradicted by Section 29(2) of the law, which says that "Zulässig sind die Einräumung von Nutzungsrechten" [granting of usage rights is permissible].
By default, the ability to transfer rights implies the ability to waive the rights, so there is no need for a law specifically saying that usage rights can be waived. Unfortunately, not having such a law means that it can be difficult to un-confuse people. Fortunately, Section 33 of the German copyright law states some consequences of the situation "wenn der Inhaber des Rechts, der das Nutzungsrecht eingeräumt hat, wechselt oder wenn er auf sein Recht verzichtet" [when the owner who has granted the usage right changes, or when he has waived his right]. This quote makes clear that the right to limit usage can be waived.
Examples of German court cases recognizing that a public-domain dedication waives usage rights, such as the right to stop people from copying and redistributing a program:
The Ninth Circuit Model Civil Jury Instructions, 2017 edition, Section 17.23, states a model for the text that courts give to juries:
17.23 COPYRIGHT - AFFIRMATIVE DEFENSE - ABANDONMENT
The defendant contends that a copyright does not exist in the plaintiff's work because the plaintiff abandoned the copyright. The plaintiff cannot claim ownership of the copyright if it was abandoned. In order to show abandonment, the defendant has the burden of proving each of the following by a preponderance of the evidence:
1. the plaintiff intended to surrender [ownership] rights in the work; and
2. an act by the plaintiff evidencing that intent.
Mere inaction [, or publication without a copyright notice,] does not constitute abandonment of the copyright; however, [this may be a factor] [these may be factors] for you to consider in determining whether the plaintiff has abandoned the copyright.
If you find that the plaintiff has proved [his] [her] [its] claim[s] in accordance with Instruction[s] [insert cross reference to the pertinent instructions on the plaintiff's theory of infringement], your verdict should be for the plaintiff, unless you find that the defendant has proved each of the elements of this affirmative defense, in which case your verdict should be for the defendant.
See also Section 17.19 in the 2007 edition, and Section 20.19 in the 2001 edition.
There are lawyers who make money helping people create, and comply with, complicated copying conditions. Let's look at claims made by one of those lawyers, Lawrence Rosen.
In a 2002 essay titled "Why the public domain isn't a license", Rosen claimed that a clear written dedication of a copyrighted work to the public domain doesn't actually abandon copyright. In particular, Rosen claimed that "Intellectual property enters the public domain only when it grows old" and that "There is no mechanism in the law by which an owner of software can simply elect to place it in the public domain."
Hmmm. If you see
then wouldn't you expect the lawyer to explain the contradiction?
Rosen's essay gives no hint of what the judiciary had already said. Instead the essay comes across as a lawyer helpfully correcting novice misimpressions. Let's look at the details of Rosen's argument:
In fact, there are laws against littering, and those laws put considerable limits on the ways in which you can abandon your real property. There are no laws against abandoning a copyright.
Rosen doesn't seem to understand the differences between waivers, gifts, and contracts. It's true that a gratuitous promise, a contract without "consideration", generally can't be enforced: someone who makes a promise, without being promised anything in return, can retract the promise. But this has no relevance to a gift that has been given; a donor cannot demand that his gift be returned. It also has no relevance to a right that has been waived.
This part of Rosen's essay follows his general "Public domain is evil!" theme but obviously doesn't support his "Public domain is nonexistent!" claim.
If these were the best arguments that Rosen could come up with, I'm not surprised to see judges saying that they're "settled" on the opposite position.
In a public message in 2012, Rosen admitted that "at least in the Ninth Circuit, a person can indeed abandon his copyrights (counter to what I wrote in my article)". He didn't give any further analysis of his errors, and he didn't state any reason to think that this (quite elementary) legal issue would be decided differently by any other courts. He did finally withdraw his recommendation against "public domain" dedications:
I admit that I have argued for years against the "public domain" as an open source license, but in retrospect, considering the minimal risk to developers and users relying on such software and the evident popularity of that "license", I changed my mind.