system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why does one look ugly on camera, but handsome in the mirror?

Less ugly/more handsome, whatever floats your goat.
gpt
Oddly enough, the reason you don't like how you look in photo's is because you are much more accustomed to (i.e. spend more time) looking at yourself in the mirror. This is from a little thing called the mere exposure effect, in which people develop a preference for how a thing looks simply because they are more familiar with it. 

When you look at yourself in the mirror your features are reflected back at you meaning that your right arm is on the right side of the reflection. In a photo where you are facing the camera, your right arm would be on the left side of the photo. Since we are not perfectly symmetrical a mirror image of you and a photo image of you is slightly different.  As this is not the version of yourself that you are most familiar with, you do not like how it looks as much. 

how much you dislike yourself in photo's is directly related to how much time you spend looking at yourself in the mirror.