Both your self esteem thoughts and "wild" imaginings are the same. You won't tell yourself good things you know to be true so you imagine others, it has to "out" one way or the other because you are intelligent, imaginative, creative, thoughtful, all the things you have others tell you you are.

I would go ask someone you respect how they view you and then use that to help yourself/your self esteem, "Well, so-and-so tells me I am too hard on myself and really smart and they are real and you, voice-in-my-head, are not, so there!"

You can think whatever you want, it's your head! Just decide you are what you have others tell you you are and assume that and look for it everywhere and it will start showing up and the hard, negative voices won't try to embody themselves anymore because there will be no room for them.

As Carly Simon put it:

. . .how to leave myself behind
How to turn down the noise in my mind
Now I haven't got time for the pain
I haven't got room for the pain
I haven't the need for the pain