Hi Marcus!

Thank you very much for your response! I'll have a look into the module you advised and leave some feedback.

Regarding your remarks:
- I am aware that leaving this proxy open is a security issue and I'm thinking about doing some basic checks like referrer. But since this setup can only proxy single files and isn't defined according to socks-standards or something, I don't think this should be a real problem.
- I tried different regexes and sticked with this, since I tried some configs where I needed the host. Thanks for reminding me to change this back! :)
- I only need to proxy little images (<10k). Do you know a way to permit only those sizes for nginx to proxy?

Again, thank you very much for your answer!
Hendrik