What does it mean when a girl take a picture of a guy secretly?

Anonymous
So my friend has this woman who seems to have a crush on him. She says hi to him first. She loves to say his name and she tries to start casual friendly conversations with him. One day I was going through the door with him and she was taking a picture of herself. Her phone was really up. But when she saw us she directed her phone towards my friend and it was obvious that she was taking a picture of him. We both pretended that we did not notice. And talked to her casually while we passed her by. Why did she take a picture of him?
What does it mean when a girl take a picture of a guy secretly?
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