1. An image processing apparatus, connected to an image pickup part and a display part, in which exposure conditions for photographing a measuring object can be changed, the image pickup part comprising an image pickup section constituted of an assembly of a plurality of pixels for photographing; the image processing apparatus comprising: a photographing controller that generates a plurality of image data by making the image pickup part photograph the measuring object under different exposure conditions a plurality of times; a compositing section that generates composite image data, based on color information and luminance information of the plurality of image data; and a display section that displays on the display part a composite image based on the composite image data, the compositing section comprising: a composite luminance calculator that calculates a distribution value corresponding to an intensity distribution of lights incident on an image pickup element of the image pickup section, as a composite luminance distribution of the composite image data, based on the luminance information of each image data and corresponding exposure condition; and an accuracy determination section that calculates a value corresponding to the distribution of the light intensity incident on the image pickup element of the image pickup section based on a luminance distribution in the plurality of image data corresponding to specific points, and determines reliability of the composite image data based on a degree of coincidence of this value of each image data wherein the accuracy deteimination section determines the reliability, based on a variation of converted values calculated by correcting each pixel in the plurality of image data under the corresponding exposure condition.