To find background information and the dates when the various postage rates applied, I have consulted: (a) Stanley Gibbons' Specialised Stamp Catalogues (b) 2.
A postal service can be private or public, though many governments place restrictions on private systems.
There is some confusion on what Real Photo Postcards (RPPC) are, and how to differentiate from a printed postcard.
Real Photo Postcards are photographs that are reproduced by actually developing them onto photographic paper the size and weight of Postcards, with a Postcard back.
The Universal Postal Union (UPU), established in 1874, includes 192 member countries and sets the rules for international mail exchanges.
It was spelled that way until the 17th century, and is distinct from the word male.
If the photo is printed, you will see that it is made up of a lot of little dots, the same as a photo printed in a newspaper.
The head on this series of stamps was known as the 'Profile Head'.If the postcard has a stamp box, click on one of stamp box links below.If there is no stamp box, or a generic stamp box, go to Postcards Backs.Most Real Photo Postcards, abbreviated RPPC, have information on their backs to help in identifying the manufacturer of the photographic paper that was used by the postcard publisher.If you can identify the paper manufacturer, you can approximate the age of the old postcard.