I think where we differ is that I've never understood why simply saying "I prefer not to" isn't acceptable when it comes to declining photographs in a way it is with other things (say, declining to participate in an activity, declining to eat an offered slice of cake, or declining to attend an event). A simple "No, thanks" should be acceptable without making someone a special snowflake or selfish.
I think the lack of patience with it comes because a photograph isn't about you, and isn't really FOR you. Refusing to participate in a big family photograph is not the same as refusing to eat a slice of cake or refusing to attend an event (though that could be pretty close in terms of hurt feelings, etc., depending on the importance of the event).
A photograph is specifically a gift for the other people who might look at it.
And its impact on you can be pretty minimal. The sort of people who delight in mocking you on Facebook because of the not-attractive photographs are VERY few and far between.
So you stand there patiently, and you smile for the 2 seconds after the photographer says "smile!" and then you go away. You never have to look at the photograph itself. It doesn't *need* to really impact you.
And do you think you are the only one who doesn't like how they look in photos? No, you're just the only one who thinks that somehow you SHOULD look good in all photos, or that the world should be shaped in a way that YOUR concerns about photos should be catered to, even if the rest of us have gotten over the self-consciousness. And you come across excessively self-focused.
Honestly, the rest of us don't care that you look a little doofus-y. Your insistance on avoiding the photo just makes you seem more selfish; WE all look a little doofus-y, but we sit there and smile so that our family and friends can look at pictures later and love us from afar.
Do you like to see photographs of other people? If you have *ever* enjoyed looking at a pic of your cousins / your kid / your parents / your friends, then you need to do your part. Suck it up and smile, and then just neglect/refuse to look at the photograph afterward. Or, when you do look at it, look at the OTHER people in the picture.
I have a LOT more sympathy for people who say, "please don't take candids of me," and very little for people who won't stand in the group photo of the family for a couple of seconds.
Being rude about it is rude. Rude to the person who doesn't want to get their picture taken AND rude to the other people bcs the bully/sneak/whatever is making a fuss.
(as for digital photos--I'm personally not that worried about group family photos.)