Solo
Marty has finished his wild guitar solo during the school dance. The entire gymnasium full of people stands silent and stunned before him. The imagery shows us the reality that most, if not all people are ready for the new things to come as time goes forth. And this is a perfect example as Marty has played his guitar in a way that won't be seen for a decade to come.
Peeping Tom
Marty sees someone in a tree with binoculars and discovers it's George (the teenage version of his father) looking into a home to watch a girl undress. The imagery shows Marty that his Dad was a pervert and thus alters his view of his father in a totally unimagined way.
Original 1985
We watch as an older Biff chews out Marty's Dad George prior to Marty's time travel. Biff is blaming George for not telling him there was a blind spot on his car which Biff borrowed and wrecked. George cowers to Biff and agrees to pay the damages. Also, Marty's Mom Lorraine is overweight and appears miserable. The imagery reveals to us later how Biff had come between them decades prior in high school, but once George knocks out Biff the future is altered and George and Lorraine are happy, confident and don't take any crap from Biff.
Opening
We watch in the opening scene as the clocks which fill up Doc's lab begin to all go off simultaneously. The imagery reveals clearly from the opening sequence that this film is about time as Doc has built a time-machine out of a DeLorean he's customized.
