[BUGFIX] original image is replaced

__Tasks:__

- [ ] gather feedback for my changes
- [ ] submit changes to the documentation

__Informations:__

| Q             | A
| ------------- | ---
| Bug fix?      | yes #86
| New feature?  | no
| Tests pass?   | none
| Fixed tickets | none
| Doc           | none
For consistency I would call this exception `FilenameAlreadyExistsException`, because there is already a `ResourceLocatorAlreadyExistsException`, and conflict is IMHO a quite specific term.