Translation:I will miss you when I look at your picture.
So, if the subject is the same in both clauses, then tge subject pronoun need not be repeated, even if it is one usually used with the fiture tense?
True in this case, but not in every case. I don't know a general rule, but as I run examples in my head, it seems it is true for future and past but not for present.
אני אתגעגע אליך כשאסתכל על התמונה שלך.
אני התגעגעתי אליך כשהסתכלתי על התמונה שלך.
אני מתגעגעת אליך כשמסתכלת על התמונה שלך.
The latter is not quite right.
I think Hebrew is the only language I know of that drops only some subject pronouns only sometimes. It's difficult, but very interesting.
But it makes complete sense that you can't drop "אני" in the second clause of your third example, becuase there would be no way of knowing who is the subject (מסתכלת could be את or היא as well). In the first two sentences the subject is implied by the verbs.
I don't get why the second part in english is in present and not in future.