I want to publish my pictures with a CC-BY-NC license but I could not find a tutorial how store this information with my JPEG metadata.
Is there a best practice? Do services like Flickr, Google+ or Facebook read this information?
If you are using Photoshop you can go to File > File Info - This will allow you to include copyright data in the JPEG Metadata.
I am not aware of how services like Flickr, Google or Facebook handle metadata so I cannot comment there.