Questions & Answers about Vidim se u ogledalu.
In Croatian, the subject pronoun is often omitted because the verb ending already shows who is doing the action.
- vidim = I see
- the ending -im tells you the subject is I
So Vidim se u ogledalu is completely natural without ja.
You could say Ja se vidim u ogledalu, but that usually adds emphasis, like I can see myself.
Se is a reflexive particle. In this sentence, it shows that the action goes back to the subject:
- vidim = I see
- vidim se = I see myself
So se is what gives the idea of myself here.
It is very common in Croatian with reflexive verbs and reflexive meanings.