I don't think anyone would particulary mind that, however, this does raise an interesting point regarding multimedia.
If people upload a screencap, or the episode, that property does belong to Seven etc. and that sort of stuff. However they seem happy enough about that.
However, to complicate things a bit down line it does create this vacumm that it is alright to take someone cap or episode to take a still from and turn it into your own piece of artwork without asking or crediting/thanking them for the picture, but it is then not correct for someone to take your avatar and upload it as there's without accreditation.