For those who are confused as to what all the Blu-Ray/DVD stuff is about...
http://www.tbs.co.jp/anime/k-on/disc/disc_1.html
For the reference to the season 1 DVD covers. I'm wondering though if the picture taken that was the 7th DVD cover occurred in the 2nd or the 3rd year of high school in the K-On! storyline? Since it was the final scene in the episode, and they didn't make it clear, I'm not sure if the scene was a flashback or not...
Also, Ritsu still didn't explain why that hand was on Yui's shoulders back in episode 3. Guess its just a spur of the moment thing.