While I'm not an attorney duly licensed to practice before the state of California, I have worked for them for over 15 years. I speak from this experience as well as my legal research certificate from UCLA Extension. I did find and take a quick breeze through some of the copyright statutes. So, here goes.
I don't think it matters where the Dark Shadows materials comes from whether it be from a video of a TV recording, a DVD recording, a live TV feed, CD, MP3 file, record, picture from an old magazine, print media or whatever, wherever. Dan Curtis Productions, Inc. owns the rights to Dark Shadows. Print media (novels, magazines, books, photographers) also own their works which depicts Dark Shadows, its characters, etc. They or their agents can choose to exercise those rights under U.S. Copyright law or not to exercise those rights. It's their decision to do so. Copyright enforcement can also be applied to fan fiction that is published on the Internet, not just pictures.
Nothing after 1923 is in the public domain. This is an important fact to remember. There are a few things that are but it's because they let the renewal lapse. I don't think DCP, Inc. or its agents are going to let that happen anytime soon.
There is a fair use clause which is unique to U.S. Copyright law. However, it's complicated and don't think I want to make any blanket statement(s) and say one could do something and then it turns out to be incorrect. It's best to do your own research with the U.S. Copyright code and make your best decision based on that reading. It's available on the Internet.
It is a true bummer when one of us appears to be singled out for copyright infringement enforcement. However, it does appear that the Powers that Be seem to be consistent when it comes to videos and/or video sites. None of us are safe from a cease and desist request. How they would ever enforce it with the cap sites is beyond my imagination but they could choose to do so. I just don't think it would be very cost effective for them to make that choice and cease and desist every one of us in web land.