The piece of text I have is as following:
"They are all looking at the photographer except the woman. In the background, there is a couple who look/looks? very shocked."
So should it be looks or look?
You may like the following explanation by Grammar Girl.
Grammar Girl : Collective Nouns :: Quick and Dirty Tips ™Singular or Plural Verbs?
Let’s use the collective noun “couple” as an example. When you are thinking of the couple as two separate people doing separate things, you would probably use a plural verb. For example, you would say, "The couple are vacationing separately this year," because they are two different people doing two different things. On the other hand, if you're thinking of the couple as a single unit, you would probably use a singular verb. For example, you would say, "Each couple is going to Bermuda on a different day." You just have to use your best judgment, and even though this seems tricky, the good news is that you can never really get it wrong because 1) there is no real rule, and 2) you can always just assert that you were thinking of the couple as individuals (or a unit) if someone questions your verb choice (2).