I breathe, don't believe me find me. I have the five senses of sight, hearing, tasting etc. You have now acknowledged my existence, If everyone was your own perception then everyone would have something more to them. Your brain could not merely make humans off your mind. If you can feel it. hear it. and see its organs inside then You are alive. Your own brain can't generate the function to run a world more or less make a human from your mind. Sure you can imagine but thats only a blur image. Sure this may not prove I exists. But i have every right to be and I see no way to see how I am not.