Those who are caught discarding litter in areas that are not designated for waste disposal must pay a fine.

에서 

discarding litter in areas that are not designated for waste disposal은 ~하는 이라고 해석되는데요,

수식어로 보면 되나요??

즉, Those를 1.(who are caught)
2. (discarding litter in areas that are not designated for waste disposal)

가 꾸며 주고 있는 것으로요..

"Those (who are caught) (discarding litter in areas that are not designated for waste disposal) must pay a fine.

   주어                                                                                                                                   동사   목적어

이렇게 되면, discarding 앞에 who is 가 생략된 것인가요??

아니면, caught와 같이 연결된 것인가요?

느낌 상 해석은 되는데, 문장에서 저 부분의 문법이 궁금해서  올립니다.