Solved problem with DYNDNS, links and pictures:

As others did, I got the problem that WordPress worked well inside the lan, but was not reachable from the outside world. Second problem was that the pictures where not showing up. Here are the instructions to fix that.

1. Be sure that your NAS can be reached from the internet and your web station is up and running.
2. Get mySQL up and running.
3. Install phpMyAdmin
4. Install WordPress
5. As I couldn’t change URL (to eiseler.synology.me) in the WordPress settings, I followed: how to change url directly in he database
6. As I found out, this doesn’t change the internal links to pictures and media. Install Update URLs and change the URLs from internal ips to dyndns.
7. When adding new pictures I change the “Link URL” when adding them

(Keywords: Problem with synology NAS, wordpress, dyndns, links and pictures from internet)