On June 6, 1974, the USPS issued a set of 8 stamps that marked the 100th anniversary of the Universal Postal Union, an entity that includes the postal administrations of more than 150 countries. UPU members cooperatively deliver mail almost everywhere. The eight stamps display the theme of writing and reading letters, taken from the paintings done of eight international recognized masterpieces.

RAPHAEL: From the Italian artist Rafael's "School of Athens" in the Vatican. Raphael gave Heraclitus the features of Michelangelo.
HOKUSAI: From "Five Feminine Virtues" by famed Japanese artist Katsushika Hokusai.
PETO: From "Old Scraps" ("Old Letter Rack") by American artist John Frederick Peto.
LIOTARD: From "The Lovely Rader, " By famed Swiss painter Jean Etienne Liotard.
TERBORCH: From "Lady Writing a Letter," by Dutch artist Gerard Terborch.
CHARDIN: From "Young Boy With A Top," by French master Jean-Baptiste-Simeon Chardin.
GAINSBOROUGH: From "Mrs. John Douglas," painted by English artist Thomas Gainsborough.
GOYA: From the portrait "Don Antonia Noriega," by Spanish artist Francisco de Goya.

These 8 covers carry Fleetwood cachets, with their trademark colorful design and explanatory text on the back.  All are unaddressed and would make a great addition to any FDC collection!

Check the scans for details.