To my surprise, there seems to be a rather large online community that is enjoying APOD content ... without realizing it originates from APOD.
So I just joined Google Plus actively for the first time this week because I had heard that there was an active astronomy writers community there. What there appears to be is an "Astronomy" "circle" where indeed several prominent astronomy writers appear to be members. Anyway I was checking my Google Plus "Stream" of posts going by, mostly from this circle, and to my surprise, APOD content came by. Well it had a thumbnail APOD image and the APOD text verbatim. It was posted by an account named "Earth". Looking at it more closely, though, this Google Plus post never mentioned APOD explicitly nor linked back to the APOD from which the text was taken. What it does do is list the astrophotographer and cite the source as "http://www.nasa.gov/".
I found that disappointing. I posted in the comments that APOD should be cited explicitly ... and never got a response. So I sent a personal message to "Earth" saying essentially that the APOD text is technically copyrighted (although NASA and the APOD mirror sites can us it for free) and so in exchange for a link to the right APOD, they can continue on as they were. I think this is OK since they are using only a thumbnail of the image. Still no response, as yet. Here's the kicker -- this "Earth" user is followed by over 47,000 Google Plus users. Wow -- that's getting up near APOD's daily page views to its main page.
Now I like and encourage APOD mirrors, on Google Plus or wherever. What I don't like is that APOD gets no credit there. If people have any thoughts on how I can change this, please volunteer them. Perhaps if several people sent in similar complaints, "Earth" might hear the group -- a situation perhaps similar to "Horton Hears a Who".
After this experience, I went back on Facebook, a site I am a little more familiar with. I searched anew to see if the same thing was going on there. Turns out it is, to a lesser degree. First and foremost is the excellent Facebook APOD presence run by bystander which is closing in on 10K followers. (Yea bystander!) But there is another presence called "astronomy picture of the day" (lower case) that is run by "Artist" that, although clearly mentioning APOD, does not link back to the relevant page(s). Oddly, this Facebook page(s) have (just) OVER 10K followers. Now this Facebook user sometimes runs non-APOD images and text, so the situation is a bit more confused.
Does anyone know of any other uncatalogued APOD mirrors that have a large following? I guess one definition for "large" is 10K or more.
One advantage of asking these "new technology mirror" sites like Google Plus to link back to APOD is that APOD can then receive credit and so be on firmer ground with NASA, for example.