While I can't specifically help you or tell you what to do when it comes to your dad, I can tell you from personal experience that I fully relate to the way you feel about yourself.
I've always had this strange tendency to compare myself to everyone in such a way that I always come to the conclusion that I'm inferior. I've always told myself that whatever bad things come my way is my fault because, just like you, I thought I wasn't good enough. BUT THAT ISN'T TRUE!!! I've learned that, however corny and spacey it sounds, we all have our own qualities. And just because you might not be the best-looking of all doesn't mean you're ugly. Just because you might not get the best grades doesn't mean you're dumb. It is your task to find the things you excel at. And I know how hard it is, I've only started looking for my good qualities less than a year ago. I found that I'm friendly and accommodating. I've even found out I'm a pretty good driver; you also have to praise yourself sometimes for the little things that may seem insignificant and give yourself a break! Ask your friends for their opinion!
Oh and the giving yourself a break part... I know how that sounds. My friends told me this many times and I always said to myself: how can I when I keep messing stuff up? But you will start seeing the good in yourself if you really want to. I've even turned from a tried and true pessimist to a slightly(!) optimistic person.
I hope that this helps..
All the best!