Beginning (in America) as a mere 19 words in the constitution, "copy right" was originally intended 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" (Article I, Section 8, Clause 8). In essence, Congress understood there needed to be a financial incentive for creativity, but it also understood that after a certain point, that balance needed to tip more toward the public good. Over time, American "copy right" has evolved from a mere 19 words to 366 pages of law. As this might suggest, copyright has become convoluted. But the slightly good news is, there are only a few critical sections that really affect educators. Knowing the core concepts of copyright will often guide you to making cogent and law-abiding decisions.
Copyright grants monopoly to any "fixed" and "creative" work. A photograph is obviously copyrighted. And so is a digital photograph; (it's fixed on a computer). A grocery list is generally not copyrighted because though it may be fixed, it's not creative. A taxidermy animal is copyrighted. A phone book is generally interpreted as not copyrighted because it's not creative. Microsoft office is copyrighted, or an iPhone app is copyrighted; but the something like gene sequencing is not copyrighted (rather it's patented.) Clothing designs are definitely copyrighted; so are buildings, and roller coasters. A classroom assignment is generally copyrighted, but a course outline template, assigned by administrators, is generally not copyrighted. It may be fixed, but it's not creative.