あなたに　for you そのイベントの写真　 pictures of the event を　particle とってあげます。will take ( for you ) あなたに、そのイベントの写真をとってあげます。 あげます　is future tense of あげる.

If you ask about "I will take pictures of the event", it is easy, 私は（I ） イベントの(of the event) 写真を (pictures) 撮ります（will take) However "I will take pictures of the event FOR YOU" is rather difficult to translate into Japanese. ++++Reason1: Japanese word for "you" changes depending on relationship between the speaker and "you", あなた、きみ、おまえ、＊＊さん Who is "you"? There is no general "you" in Japanese language. So without knowing it , we cannot translate it. Remember, Japanese is a "RELATIONSHIP" heavily depending language. ++++Reason2: This is more important reason. In Japanese conversation, we try NOT to say words for "you" as possible. My friends never use words like あなた、きみ, when they call me. This means there is NO Japanese word directly corresponding to "for you" in English . At least, between I and my friends, there does not exist such a word . If my friend says "あなたのために／きみのために、イベントの写真を撮っておくよ", I feel creepy in my back. Then what would my friends say when he wants to say "I will take pictures of the event for you" I think it can be like this: 「あのイベント行きたかったんでしょ。じゃあ、オレ(male)／私(female)が写真、撮っておくから」 literally translating. "You wanted to go to that event (and I know you can't), then I will take pictures of the event ( and keep them)." 撮っておく =　撮りて　＋　おく おく： keep, put, let it stay. this word "おく" implies "(keeping them ) for you" and ”から" of "撮っておく" also implies "for you" The "から" here means "because" This implies "Because I will take pictures of the event (it will be all right for you).,