I relate to your inability of posting pictures due to a mix of "who the hell cares?" and anxiety.

Two things:

One, you don't need to post pictures, do you? I don't get why people feel the need to fill up their social media with pictures of them doing mundane stuff. There's no need for it and you shouldn't feel obligated to follow that trend. Live your life, that's more important than taking pictures.

Two, this might be harsh, but as with a lot of forms of anxiety, you need to realize people in general don't really care enough about you to 'make fun of you' oe anything. One of the most common forms of such anxiety is when talking to a stranger, for example talking to a cashier. Truth is, that cashier isn't gonna care about what you say, you are just a random customer in a slew of customers that day. If you screw up, or don't look 'good' in a photo, people won't care. They'll just move on.