In this paper we present two algorithms modifications of projective-recognition of the plane boundaries with one concavity. The input images are created with orthographic pinhole camera with a fixed focal length. Thus variety of the possible projective transformations is limited. The first modification considers the task more generally, the other uses prior information about camera model. A hypothesis that the second modification has better accuracy is being checked. Results of around 20000 numeral experiments that confirm the hypothesis are included.