Official comment

No there isn't a single API that would help you with this, but with a bit hacking it should be doable. Note that this needs to be done as the user since only a user can update their own profile.
Basically you need to
- Get the users current profile `GET /contact/user/{user_id}` (let's call the result `p`)
- Get the users avatar from `p.image.link` (should be a URL)
- Alter the image
- As the user: Upload the image - get the ID - links call it image_id
- As the user: `POST` to `/contact/{p.profile_id}` the value `{"avatar" : <image_id>}`.
Cheers,
Brian