Nicole K.’s explanation based on actor or object focus is correct.
Both words have “manood” (to watch - a movie, the TV, a show, or an event) as their root and “nanonood” and “pinapanood/pinanonood” are both in the present tense. You may compare their use in these two sentences which follow the active and passive voice structures of English.
Active: Si John ay nanonood ng pelikula. = John is watching a movie.
Passive: Ang pelikula ay pinapanood/pinanonood ni John. = The movie is being watched by John.
Filipino sentences, however, may be formed differently from the standard active or passive voice structures of English. Consider these two sentences, which are practically saying the same thing:
Nanonood ng pelikula si John.
Pinapanood/Pinanonood ni John ang pelikula.
Now compare them to the Active and Passive voice examples given above. Notice that there are now no “ay”s, but correspondingly, exactly the same words are used, just in a different arrangement.
BTW, most Tagalog/Filipino speakers would say it a “pinapanood”, but you may hear others say it as “pinanonood”.