Posting pictures of others

Can you freely post pictures of others and others on e.g. Facebook?

You should ask people before you post pictures, videos etc. of them, but most people don't.
If you have a funny picture of your friend, you should ask yourself "Would my friend like to have this picture on the internet for the next 20 years?" and then ask your friend for permission before you post it, but what you really think is "This is funny, of course I'll publish it".

Would you, for instance, like to have this picture of yourself on the internet?