If you post something about yourself online, odds are that a future employer will see be able to see it too. How would you be? When you get to know someone, chances are you have googled them.
Is that an invasion of your privacy? Not really. After all, you decide what is on the internet about yourself, whether it be a profile, photos, videos, ... You also decide whether those things are only visible to your friends, or to the whole world.
That's why it's a good idea to google yourself before applying. Do you only find things about yourself that you like? Great! But if there are photos here or there that you would rather not show your future boss, then delete them or adjust the privacy settings of your profiles.