The sentence (from the first episode of Death Note)
means something like
If the written person’s face is not in your head, there will be no effect.
For this post I'm struggling to understand "書く人物":
The translation provided is something like "person who is written" or "written person's". But how would we know this doesn't just translate to "person who writes" or "person who will write", since 書く is in the non-past (and non-passive) tense? Is it just through context alone?
If instead of 書く人物 we used instead 書かれた人物 (to more closely mirror the way things are idiomatically spoken in English), would this just be total nonsense in Japanese, or would it have some other different meaning than "written person"?
NOTE: This question also discusses this sentence, as well as the inherent ambiguity of Japanese relative clauses. For this question I'm more focused on how the tense/conjugation of 書く impacts the way we interpret this sentence.