The owner, and those who are delegated to run the site on the owner's behalf, have the
absolute right to specify what is and what is not acceptable on the site. However...
Forgive me if I'm missing something here, but
if the images are stored on a third-party server, then the PPRuNe server will not get involved in the process of transmitting the
images at all. Certainly PPRuNe will have to hand out the URL (which compared to the size of most posts is pretty small), but once it's handed the URL out, then it's up to
your PC to fetch the image
directly from the third-party server on which it resides (which is, I assume, one of the reasons why you have to have the image on a separate webserver to start with) -- but the image itself never goes near the PPRuNe server at all, surely ?
Again, as the DCP says, if it's policy not to post images then that's the end of it, but I don't actually think that linking to images will substantially affect server bandwidth. Or am I missing something very obvious... ?