Now we are getting into grey territory. While it's usually within the law to photograph anything in a public space, uploading to social media is a different beast.    If you don't get explicit (preferably written) consent, you should best blur out any license plates. To be 100% on the sure side, avoid posting people's faces, too. You can deal with the objection in three ways; before, during, and after. Or, as we say in street car photography; it's easier to ask for forgiveness rather than for permission.    You better believe it, owners of exotic, vintage, or modern supercars are pretty dang used to them being photographed all the time.    Even if only with a hand gesture, asking for permission conveys respect and class.