The two pictures with lots of portraits and few people are of Christ Church. Harry Potter fans rejoice, this is where the movie was filmed. It is pretty incredible, and has rules (that are enforced by a fine) for anyone who takes pictures of/while (?) people are eating.
The other two pictures (balcony shot and group picture--in gowns) are of Magdalen (pronounced Maudlin). The guys in the balcony are singing "grace" in latin. We (a group of us who were visiting) were very touristy--and probably broke some rules--by taking photos during the prayer. I would feel guilty about it, but I don't understand what they are saying anyway, so I can't really "Amen" with them in any honesty.