Letter Library: the type specimens of the world

When I add entries for external specimen scans to our catalog, I prefer using reliable sources, where links are likely to remain valid for many years to come. An example are national archives, which provide permanent URLs specifically for that purpose. I also trust links to the Internet Archive or the websites of organisations like The Letterform Archive, St. Bride Library and so on. I have so far excluded Flickr albums as it is a paid private service and any user uploading images could easily just leave the platform at any time, making all albums they uploaded inaccessible. But there are some interesting type specimen albums on this platform. So should it be included as a source worth cataloging?