1. An image processing apparatus, comprising: a first receiving portion receiving a first image of an object taken under a prescribed illuminating condition; a second receiving portion receiving a second image of said object taken under an illuminating condition different from said prescribed illuminating condition; and an eliminating portion eliminating an effect caused by an outside light using said received first and second images, said eliminating portion including an adjusting portion adjusting at least one of said first and second images to equalize brightness differences of said first and second images, and a calculating portion calculating a difference between said first and second images adjusted by said adjusting portion to have the same brightness difference.