While I was in Germany last time, I had a go on the stamp vending machine at Deutsche Post.
Purchased: 26th August 2013
The value of the stamp is printed at the moment you purchase it, according to your selection. These stamps represent the main postal rates in Germany at the moment: 0.45 (euro) for a postcard, 0.58 for a standard letter, and higher values for larger letters (according to dimensions, I think; there is a measuring scale on the vending machine).
There are 2 designs currently in use, as shown above.
- 0.45 and 0.90: Post Tower – Bonn
- 0.58 and 1.45: Brandenburg Gate – Berlin
The design that you receive is random, it is not tied to a value, so you might get two stamps of the same value but with different designs. (Or maybe they alternate, I don’t know, this is yet another philatelic specialism that I know precisely nothing about.)
If you don’t have the correct amount, German stamp vending machines give change in stamps. (In other countries, you might receive change in coins.) The stamps you receive are either according to the current postal rates, if you are due enough change, or on stamps to the value of your change, if it is a lesser amount.
If you end up with a load of small amounts, you can still use these on your letters. To make up the postage, you can choose a custom amount instead of one of the standard rates, so you don’t have to overpay postage.