This service has been created by Matograine. Many members of Ğ1 libre currency helped:
Ğ1 (pronounce "Jüne") is a libre currency. It means that it is created on a regular basis, equally for all members, and that the monatary issuance rate stays the same among human generations. More info on English threads from the monnaie-libre.fr.
These tree characters are called "checksum" or "control sum". They are separated from the public key by a colon (":"), allow the wallet software (i.e. Cesium) to verify that the public key is consistent. It is especially useful when a customer wants to copy your public key by hand, since manual errors can be detected.
The best size for the image is 900x900 pixels. a square image will be resized. A non square image will be truncated by a square centred on the image before being resized at 900x900, then reduced to the size of the sign.
The Git repository for this project is on the Duniter project Gitlab forge.