“Mark [Frost] and I figured out the best thing would be to have Cooper become passionately involved with Audrey. To have a big affair. That was what all our mail was about, and that’s where it was all headed.” - Harley Peyton
You may see there’s a sign above them where you can read “to our graduates”. Graduates are usually involved in a graduation (obvs) and they’ll graduate in legacy.
So this pic we can assume was taken after they filmed the episode.
In the picture above we can see Maya and Harley. If you look closelly the chlothes she’s wearing in the first picture are very similar to this one so we also can assume this picture was taken after the same episode.
Also in the Lucas and Harley picture, Peyton is with the same t-shirt he was wearing in the picture with everybody, even if he’s wearing a shirt/jacket with it.