Say you've spent a considerable amount of time, and perhaps some money as well, documenting a set of families. The work has paid off, and one of the rewards is to share it with people who may be living descendants of those documented by your research.
The problem is that once you publish your research on a public web site of your choice, nothing prevents other (well-meaning) people—often your relatives!—from copying your work without attribution and incorporating the metadata and images related to the records you uncovered into their trees.
In some areas of human intellectual endeavor (e.g., academic publishing), this would be considered plagiarism. In other areas Creative Commons or other licensing may be used to allow reuse but to require people to give credit to the authors of the documents or other artifacts (e.g., software source code).
How should genealogists approach this situation? I can imagine several possible tactics, each with its own trade-offs:
Don't publish anything in machine-readable ways. Making it difficult to incorporate information into other people's trees will deter some people; those who are not deterred are much more likely to cite the source. The downside is that fewer people will see the information because it will not be as easy to find, and that re-typing information from it (using it as a source) will be a source of errors.
Publish machine-readable information, but do so with privacy settings that require others to ask for documents. This makes it easier to keep track of who gets the information, and you might be able to ask them to attribute to work appropriately. No guarantees, of course.
Publish machine-readable information publicly, and contact those who use your information after the fact to ask them to give due credit. They are less likely to bother, but it does benefit more people who have access to the evidence you have collected.
Don't care about who does what. After all, as we used to say in an early (and successful) non-genealogical research project I was involved in, "your ideas will be stolen, whether they are yours or not."
I am curious to know which of these, or what other, solutions people have adopted, and if there are ways in which we can change best practices in the field to reward the effort that goes into our research.
Many of the excellent answers below had assumed a more polished form of publication than I had intended to convey in my question. I was referring merely to the accumulation of historical records associated with people in a tree, such as one that might be maintained at Ancestry.com. Clearly the copyright-able aspect of this is not the individual record, but the accumulation of such records to document an individual's (or a family) history. My gut feeling about this is that since it may have taken a considerable effort to put this together, that effort should be recognized. That was the point of my question: how best to protect that intellectual (and modest financial) effort?