Self-Image - The idea, conception, or mental image one has of oneself. Self-Esteem - Respect or favorable image of oneself (Random House Dictionary)
Self-image is how you perceive yourself. It is a number of self-impressions that have built up over time: What are your hopes and dreams? What do you think and feel? What have you done throughout your life and what did you want to do? These self-images can be very positive, giving a person confidence in their thoughts and actions, or negative, making a person doubtful of their capabilities and ideas.
Surprisingly, your self-image can be very different from how the world sees you. Some people who outwardly seem to have it all (intelligence, looks, personal and financial success) may have a bad self-image. Conversely, others who have had a very difficult life and multiple hardships may also have a very positive self-image.
Some believe that a person's self-image is defined by events that affect him or her (doing well or not in school, work, or relationships.) Others believe that a person's self-image can help shape those events. There is probably some truth to both schools of thought: failing at something can certainly cause one to feel bad about oneself, just as feeling good about oneself can lead to better performance on a project. But it cannot be denied that your self-image has a very strong impact on your happiness, and your outlook on life can affect those around you. If you project a positive self-image, people will be more likely to see you as a positive, capable person.
However, it's important that your self-image be both positive and realistic. Having a self-image that is unrealistic can be a drawback, whether that self-image is negative OR positive. Sometimes having an occasional negative thought or criticism about oneself can encourage change, hard work, growth and success. Sometimes having too positive an image of oneself can encourage complacency, underachievement, and arrogance. Finding the balance between feeling positive about oneself but having realistic goals is important.