The best method is to simply ask for and receive written permission from the copyright holder. The problem though, is that depending upon the source of the photograph, it is not always evident who the copyright holder is. Publishing a photograph, or having a photograph in ones posession alone does not imply copyright ownership. The copyright belongs exclusively to the orginal photographer at the moment he or she takes the photo, and remains exclusively theirs unless they expressly (in writing) pass (or share) this right to another party, Their copyright ownership remains in effect until the work passes into the public domain - usually 70 years after the death of the author (with some exceptions depending on the date of publication).
Having said that, U.S. copyright law does not automatically guarantee that the copyright holder has exclusive rights to their work in all instances. In fact, the courts have ruled time and again that copyright laws were not established to protect the rights of the copyright holder – their purpose is to encourage creative works which would benefit society by providing limited protection of that work. This is a crucial point to keep in mind. Copyright law is meant to establish a balance between the rights of the creator and the public’s interest, but when in conflict, the balance tips more heavily toward the public’s interest, which is often contrary to what the creator believes to be fair or just.
Article I, Section 8, clause 8, of the United States Constitution states the purpose of copyright laws is “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.”
The limits of a copyright holders rights are further defined in the Copyright Act itself. One aspect of copyright law that is of particular interest to Wikitree users are the sections of the act which define ‘fair use’. The purpose of the Fair Use Doctrine is to allow for limited and reasonable uses of copyrighted materials as long as the use does not interfere with owners’ rights or impede their right to do with the work as they wish. Fair use has little to do with what we may think is fair, and everything to do with keeping the balance tipped in favor of the public interest. Fair use is in place for the greater good, to allow copyrighted works to be used without permission for the benefit of the public.
Section 107 reads in part: “the fair use of a copyrighted work, including such use by reproduction in copies or phonorecords or by any other means specified by that section, for purposes such as criticism, comment, news reporting, teaching (including multiple copies for classroom use), scholarship, or research, is not an infringement of copyright.
In determining whether the use made of a work in any particular case is a fair use the factors to be considered shall include—the purpose and character of the use, including whether such use is of a commercial nature or is for nonprofit educational purposes; the nature of the copyrighted work; the amount and substantiality of the portion used in relation to the copyrighted work as a whole; and the effect of the use upon the potential market for or value of the copyrighted work."
Given these directives, I believe that it would be extremely difficult for any legal scholar to conclude that republishing a copyrighted photograph of an ancestor or a gravesite on Wikitree - which is a non-commercial website (as stated in the Wikitree TOS) dedicated to scholarly pursuit, education and research for the public good - would in any way shape or form, infringe on the photographers copyright. On the other hand, if Wikitree or the profile manager who posted the photograph were to change course and begin to use these photographs for financial gain (for example publish and sell a book which included the photos or charge a fee to access them on the website), the copyright owner would have legal reason to demand compensation for their work.