Numista now has some pages to describe the mints. See for instance:
These pages are available either via the big list of the 3100+ mints currently listed on Numista:
or via the coin pages, when the mint is referenced, for instance:
The work to add details and mintmark pictures about all the mints is still in progress. Feel free to participate by opening a ticket on the forum about the "Numista coin catalogue" and tick "creation or modification of a mint"