The answer provided by Elaine Martin is the best place to start in answering your question. Depending upon the context of the issue, however, there may be more to take into consideration.
In the context of immigration, if a person is wishing to prove the existence of a marriage that is problematic according to Department of State rules, it may be advisable to complete another wedding ceremony.
If a person is wishing to disprove the existence of a marriage, it may be advisable to complete a formal divorce. For example, in the context of immigration applications, if the couple considered themselves to be married and identified themselves as married on immigration-related documents, then it may be advisable for the couple to complete a formal divorce before either were to marry again, notwithstanding any quarrel the Department of State might have about the legal status of the initial marriage.
[As contemplated by Avvo policy, this response is intended as general information and not specific legal advice, and this response does not establish an attorney-client relationship.]
David N. Soloway
Frazier, Soloway & Poorak, PC
1800 Century Place, Suite 100
Atlanta, Georgia 30345