Are there reliable algorithms to detect elementary 2D figures?
Circle, ellipse, square, rectangle, triangle. In the simplest form, the task may be formulated as follows. There is an empty background (black or white) and one of these figures (filled or contour). The figure may be of any size, any proportions, and located anywhere. The method should determine what it is, its parameters and coordinates.
Sounds good. The idea is to find a contour, then try and reduce the number of points in the polygon. Looks like a ready solution. Thank you.