The stamps were issued for use in the Aegean islands of Caso (Kasos) by the Italian authorities between 1912 and 1916 during their occupation of this Greek territory.

Here are some key details:

• In 1912, Italy invaded and occupied several Aegean islands belonging to Greece, including Caso.
• To provide stamps for the occupied islands, Italy overprinted existing Italian postage stamps with the name “CASO” along with new values in Greek currency (lepta and drachmai).
• The first Caso overprints in 1912 were applied to the current Italian definitive series depicting King Victor Emmanuel III.
• Additional overprinted issues followed in 1913, 1914 and 1916 using stamps originally from Italian offices in Turkey.
• The overprints were typographed in black or red ink in a variety of styles and layouts on the base Italian stamps.
• Denominations ranged from 1 lepton up to 5 drachmai to meet local postal rates under Italian administration.
• Despite being in use for only about 4 years until 1916, over 50 different overprinted stamps were produced for Caso.
• The Caso issues are quite scarce and popular among collectors of Italian occupation stamps from this era and area.

While relatively obscure, the Caso overprinted stamps provided temporary provisional issues for mail service during Italy’s short-lived occupation of this Greek Aegean island before its return to Greece after World War I.