Many people confuse plagiarism and copyright infringement, but they are not the same thing. You can plagiarize someone's work without committing copyright infringement; you can infringe upon someone's copyright without plagiarizing their work. Plagiarism is about the failure to properly attribute the authorship of copied material (whether copies of ideas or of text or images). Copyright violation is about failure to get permission (if required) to use a work.
"It is important to distinguish between infringement of copyright and plagiarism. In an academic setting, copyright law really only protects the expression of ideas (the specific words and images used), not the actual ideas themselves. If actual ideas are copied, this is plagiarism but not copyright infringement, and it is unethical, but not illegal. If you were to take a work that sits in the public domain, and change it around a bit and call it your own, you are not breaking the law, but it is plagiarism. However, if you take a copyrighted work and claim it as your original work, it is both copyright infringement and plagiarism. If you take a portion of a work that is copyrighted, change it around a little bit and insert it into your own work without attribution, you are definitely plagiarizing; in addition, depending on how much you use, this could either be fair use or an infringement of copyright." - Robert Harington, on The Scholarly Kitchen blog
1. Plagiarism is a violation of academic norms and a matter of academic integrity but not illegal; copyright infringement is a matter of federal law and is punishable as such.
2. Plagiarism is an offense against the author, while copyright violation is an offense against the copyright holder who may not be the author but may be some other entity, such as the publisher.
3. Plagiarism can occur when ideas are copied, whereas copyright violation occurs only when a specific fixed expression is copied. Mere ideas are not protected by copyright law.
4. Plagiarism concerns properly apportioning intellectual credit, whereas copyright is concerned with properly compensating someone for use of their property where such compensation is required by law (e.g. no exception such as fair use applies).
Citing: The rules for citing your sources are fairly straightforward. The following items taken from other sources must be acknowledged:
1. Direct quotations
2. Ideas from other sources, whether paraphrased or summarized
3. Facts that are not considered common knowledge (facts such as the dates of important occurrences, are considered common knowledge and usually need not be footnoted)
Whenever you are in doubt about a particular item, cite it! This serves an important purpose in addition to preserving academic integrity. Along with your bibliography, it indicates to your reader the extent of your research; it also allows the reader to pursue particular aspects of your topic on his or her own.
Quoting: You must be careful not only to document material taken from other sources but to indicate each and every use you make of another author's wording. For direct quotations, be sure not to omit any words or punctuation. If part of the quotation is irrelevant to your purpose and its omission does not change the meaning of the quotation, you may replace that segment with an ellipsis. Place brackets around any word or comment you add within the quotation.
Paraphrasing and Summarizing: At times, you will be paraphrasing or summarizing an author's idea. Any paraphrases or summaries that you do make should be completely in your own words and sentence structure. The surest means for achieving this end is not to look at the original while writing. Inserting synonyms for an author's words into his or her sentence structure is just as much plagiarism as unidentified word-for-word quotations. Integrating paraphrases and summaries fully into your own style has the virtue of demonstrating your clear comprehension of the subject matter; it also makes for a more unified and readable essay. Note that when paraphrasing or summarizing, you will still cite the author’s name and page number as a way to acknowledge your use of the source.