There are innumerable ways to express conditionals, so even if there are standard ways to translate some syntactic structures into logical notation (e.g., "If A, then B" = "A only if B" = A → B), you can only get so far with these.
Also, not every sentence that seems to be a conditional is actually a conditional. Consider the difference between "Men are grumpy when they're hungry" and "Men are bachelors when they're unmarried" which have the same syntax but different logical form.
So you need 2 things. First, a way to tell if a sentence is really conditional, and second, a way to tell which of the conditions in a conditional sentence is sufficient and which is necessary.
The easiest way to do this is to draw a truth table for your sentence. Basically, you have to ask if the sentence you're considering is true or false for every possible distribution of truth values for it's clauses. For this sentence:
Raimundo appears in every photograph that Yakira does not appear in.
You have to consider what happens if:
R appears and Y does not = T (Both clauses obtain)
R appears and Y appears = T (1st clause obtains but second does not)
R does not appear and neither does = F (2nd clause obtains and 1st one does not)
R does not appear and Y does = T (Both clauses are false)
When only one of these possibilities makes your sentence false, and it is one in which one of the clauses is false and the other is true, you know that you're dealing with a conditional sentence. The false clause in that possible world is your necessary condition, the true one is a sufficient condition.