Had to go and look up that term, and I'm not sure whether I should thank you or go and bleach my eyeballs. The Guardian article noted that there was:
"Furthermore, all of GCHQ's work is carried out in accordance with a strict legal and policy framework which ensures that our activities are authorised, necessary and proportionate, and that there is rigorous oversight, including from the secretary of state, the interception and intelligence services commissioners and the Parliamentary Intelligence and Security Committee.
Orly? Exactly who authorized the keeping of such images and why is that necessary or proportionate? Also, the use of this word, "rigorous"? I do not think that word means what you think it means.
Also, this fun little tidbit:
Rather than collecting webcam chats in their entirety, the program saved one image every five minutes from the users' feeds, partly to comply with human rights legislation, and also to avoid overloading GCHQ's servers.
Well, gosh, that's mighty white of you, GCHQ/NSA/FiveEyes. Gonna guess the it's less the former, much, much more the latter.