Taken from the Smithsonian Postal Museum website. As your example shows stamps on a postcard and not a
postal card, and is dated December 16, 1925, the bold portion of this quote applies:
Quote:
Postal cards were introduced in 1873 and could be mailed at a 1 cent rate (less than the first-class letter rate). Before July 1, 1898, postcards could only be mailed if the first-class letter rate was paid; they were first authorized for use at a rate lower than the letter rate on July 1, 1898. Thereafter, they have taken the same rate and functioned at the same level as postal cards except during the period from April 1, 1925, through June 30, 1928, when the postcard rate was 2 cents, the postal card rate 1 cent. (U.S. Domestic Postal Rates, 1872-1993, by Henry W. Beecher and Anthony S. Wawrukiewicz, p. 12)