It was described to us as a pixel attack. I'll give the description I have, because I'm still not quite sure I understand it:
The emails that you received were all from the domain “nropnews.com”. There were various email addresses and names of fake journalists attached to this domain. This kind of attack is known as pixel reconnaissance. It works by embedding a tracking pixel in a photograph or image. When the receiver opens the email, the tracking pixel is able to send back some limited information to whoever has sent the email.
It's kind of like a phishing expedition.