What is Copyright?
"Copyright may apply to a wide range of creative, intellectual, or artistic forms, or "works". Specifics vary by jurisdiction, but these can include poems, theses, plays, otherliterary works, movies, dances, musical compositions, audio recordings, paintings, drawings,sculptures, photographs, software, radia and television broadcasts, and industrial designs."
"Copyright does not cover ideas and information themselves, only the form or manner in which they are expressed. For example, the copyright to a Mickey Mouse cartoon restricts others from making copies of the cartoon or creating derivative works based on Walt DIsney's particular anthropomorphic mouse, but does not prohibit the creation of other works about anthropomorphic mice in general, so long as they are different enough to not be judged copies of Disney's."
"Copyright laws are standardized somewhat through international conventions such as the Berne Convention and Universal Copyright Convention. These multilateral treaties have been ratified by nearly all countries, and international organizations such as the Eurpean Union or World Trade Organization require their member states to comply with them. In all countries where the Berne Convention standards apply, copyright
is automatic, and need not be obtained through official registration with any government office."
"The Berne Convention states that all works except photographic and cinematographic shall be copyrighted for at least 50 years after the author's death, but parties are free to provide longer terms, as the EU did with the 1993 Directive on harmonising the term of copyright protection. For photography, the Berne Convention sets a minimum term of 25 years from the year the photograph was created, and for cinematography the minimum is 50 years after first showing, or 50 years after creation if it hasn't been shown within 50 years after the creation. Countries under the older revisions of the treaty may choose to provide their own protection terms, and certain types of works (such as phonorecords and motion pictures) may be provided shorter terms."
"If the author is unknown, because for example the author was deliberately anonymous or worked under a pseudonym, the Convention provides for a term of 50 years after publication ("after the work has been lawfully made available to the public"). However if the identity of the author becomes known, the copyright term for known authors (50 years after death) applies.""To this date, there are 165 countries that are parties of the Berne Convention."
It doesn't matter how you obtained the material, it's still considered copyrighted and you still need permission.
It doesn't matter whether or not you've credited the proper owner, it's still considered copyrighted and you still need permission.
It doesn't matter if you are making a profit or not, it's still considered copyrighted and you still need permission.
It doesn't matter if you can find other people using things without permission, it's still considered copyrighted and you still need permission.
It doesn't matter if you've edited it a little bit or made a few alterations, if it's recognizable it's still considered copyrighted and you still need permission.
dA HelpFAQ #2: Where can I find the official deviantART Copyright Policy?
FAQ #8: What are violations of the deviantART copyright policy?
FAQ #81: How can I create links to other deviants, deviations, or websites?
FAQ #217: What are "Stock and Resources" and can I use them in my submissions?
FAQ #250: The laws of my country differ from those of the United States- which ones apply?
FAQ #257: What sort of permission do I need to use someone else's work?
FAQ #809: What are DeviantArt's stock image guidelines?
FAQ #814: Should I put a signature, watermark or copyright notice on my art before submitting it?
Further Info You may also want to read this article Of Copyright & Premades by kuschelirmel
Further Info You may also want to read this article Stock and Resources: Policy Clarification by dxd
Further Info You may also want to read this article Premade Backgrounds and Group Submission Changes by CelticStrm-Stock
Further Info You may also want to read this article 10 Big Myths about Copyright!
Deeper Info and Tips for you The Berne Convention - Complete
Stop Internet Plagiarism - Article full of tips, based on experience + interesting links to get deeper into the topic
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