[Feature] cache headers for images

__Tasks:__

- [x] fix vhost headers for cached files
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes #99
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none
@alexander-schranz why fixed duration?