In Harry Potter, you can see a very important detail, maybe even a mistake. It wasn’t fixed until the third film — it’s the school uniform. In The Prisoner of Azkaban, director Alfonso Cuarón asked the kids that played the students of Hogwarts to wear their clothes as if their parents were not around — well, in the school, the kids were on their own. It’s a big contrast to the first 2 films, where the clothes looked very neat on them.
I read somewhere that he can't remember which one is actually his first picture.