Signing into Throwbackr! with Flickr will not affect the privacy or visibility of your photos on Flickr.
All sign in process works inside Flickr, with their security.
Authorising Throwbackr! will give the permission to access your photos though Flickr API.
Throwbackr! does not store any user identifiable data on its servers.
This product uses the Flickr API but is not endorsed or certified by SmugMug, Inc.