1. An image processing apparatus comprising: a storage configured for storing image data comprising data of a first model; and a processor configured for determining a final model parameter set and a final inlier scale of the first model by iteratively performing a model estimation process and an inlier scale estimation process, wherein the model estimation process determines a model parameter set from the image data by using an initial inlier scale, and the inlier scale estimation process determines an inlier scale by using the model parameter set, wherein when the model estimation process is repeated, in the repeated model estimation process, a new model parameter set is determined by using an inlier scale determined according to an immediately previously performed inlier scale estimation process, and wherein in the inlier scale estimation process, a new inlier scale is determined using a model parameter set determined according to an immediately previously performed model estimation process.