Lmaoa, I remember reading about this.

If I recall correctly, a picture shows how you appear to others whereas the mirror shows you a 'mirrored' image of yourself (e.g., your left side is the reflection's right side).

We are used to seeing our reflection, which then makes pictures of ourselves look strange.

I think selfie cameras intentionally take a mirrored image to avoid this effect. But I've never taken one because I hate looking at myself.

There's a similar phenomenon with hearing ourselves in recordings vs. as we speak.

Edit: as @ch00f@lemmy.world already explained!