Reason of Wearing Scarf

This morning, I went to Osaka Immigration Office to extend my period of stay in Japan. I submitted my application form together with some documents such as latest photograph, passport, residence card, certificate of scholarship, a seal from my faculty, and research student transcript. I was surprised when the officer asked me to fill in an additional form of statement about my reason of wearing scarf. They said it is necessary since I submitted a photograph that does not show my hair or full part of my head. I was frozen for a while, looking at a piece of paper with blank space to write down my reason.
I threw back to my past when I decided to wear scarf of so called hijab in a committed way. It was in my last year of senior high school. After finishing the final exam, I did not have any formal lesson at school, so every day I just came to school to see my friends and talked about things we wanted to do that time. We were also busy in preparing college entrance.
Before that time, I just wear hijab when I have to, for example, when I am praying, studying Qur'an, or when it was Friday of my junior high school era. At that time, my mom also do the same thing as me. No one pushed me, or even asked me to wear hijab everywhere I go or every time I meet non family members man. Even my family never force me to do so. I also never went to Islamic School where you have to wear full body uniform. I always study in public government school so no school rules that force me to cover my head.
And it just happened easily in 2012, my heart moved. I don't remember what things that moved my heart or my brain to change my behavior in dressing. I just feel it was the perfect time. Fortunately, my uniform skirt is long-designed so I don't need to buy a new one. I just need to add jacket to cover my short sleeve shirt and also a white hijab to cover my head. At that time, my mother still did not wear hijab when she went to work. And she asked me whether I was totally ready and aware of my decision, because she said some girls are not ready yet so they choose to come back (dressing without hijab) after wearing hijab every day. My mother was afraid that I just make a short term decision and become rebel again. But I convinced her, and then she, up till now, decided to use hijab as well.
So go back to the question: the reason to wear hijab
I had no reason back then, I just feel that was the perfect time to start. But after thinking again and again, reading the Qur'an more, I realized that Allah gives us the command clearly to cover our body to protect us and so we are more easily to be recognized.
I do not need another reason. My reason is Allah, and I am a moslem.