The most often cited court case on treasure trove (that is found in almost every law school textbook) is Cesarini v. United States, U.S. Dist. Ct., 296 F. Supp. 3 (1969). The Cesarini's purchased a piano at a garage sale in 1957 for $15.00. In 1964, while cleaning the piano, they found $4,467.00 in old currency inside. They exchanged the currency at the bank, reported it as income, and filed for a refund. They claimed that (1) it was not income; and (2) if it was income, it was income in 1957 (conveinently out of statute) not 1964, and finally, if it was income in 1964, it should be taxed as capital gain income. The taxpayers lost. Nevertheless, the case makes for interesting reading and addresses many of the issues raised here.
-- Bruce