Your self-image is developed from two different sources which in tandem provide the basis for how you view yourself. The first half of your self-image is the way that you feel about yourself, and your own interpretation of the events in your life. The second half is the way that others view you, and what they think of you. Believe it or not, the second half of the equation usually plays a bigger factor than the first in how we see ourselves. However, the only way to really change a negative self-image is to change how you think about yourself.
If you are subjected to constant abuse, and nobody ever tells you that you are any good, you start to believe it after awhile. On the surface it seems kind of odd that we wouldn't be able to see that if you got good grades, had a good job, and had lots of friends that you were living a good life. However, if you only hear that you aren't any good and that everything you have is just a mirage, and that nobody really likes you, then your life will be constant torture.
That is why some people have negative self-images. The answer would seem that people should start hanging around people who say good things about them, and only are there to help them feel better. While this could help, the true answer is to work on the fact that if you aren't being treated well that you have to do something about it. If you are being verbally abused, or physically abused, you need to get out of that situation. You have to take control of your life, and then go do whatever it is to stop feeling so bad about yourself.
Taking control of your life, and seeing the good things that you have, and the good qualities that you possess is a big help. It will start your mind on a path to positive thinking, and positive re-enforcement. You will be thinking good thoughts about yourself, and your confidence will skyrocket. It really is true that if you start to think positive, that other people will start to respect you more. In turn, you will see that you are a good person, and have a lot to offer.
The other part to reversing your own self-image is to realize that you really are a good person, and have accomplished a lot. No matter what anyone tells you, the house, car, education, and social life you have is something that you have earned. It takes a lot of work, and only a talented individual could do that. Just because others might be jealous, or feel like messing with you because they can doesn't mean that they are right. You have to take stock of what you have, be happy with it, and know that you did your best.
If you have a negative self-image, or know someone who does, there is hope. Positive re-enforcement can help your friend out if you know someone like that, but only that person can see what they are for themselves. Take control of your life, don't settle, and never admit that you aren't good enough, because nobody ever got ahead thinking like that.