However, there are some (early) Blues songs published before 1923 that are Public Domain (PD), so they can be used freely, recorded including lyrics, and uploaded here.
I'll try to collect them in this thread, together with Lyrics and - if possible - chords. Although the 12bar server is not located in the USA, it is safe to use the US copyright, simply because those songs are usually PD in other countries. Most of these Blues can be found on Youtube go get an idea of it.
It's not strictly all Blues, some jazz standards and bluesy traditionals are also included.

This list will be updated from time to time. Bold ones are more popular.
EDIT:
The songs are now at
http://12bar.de/pd_blues.php