Reduce the size of the checkerboard_radon.png image in the doc, see for instance in the 4.11doc: https://docs.opencv.org/4.11.0/d9/d0c/group__calib3d.html#gadc5bcb05cb21cf1e50963df26986d7c9

I have added references to the perspective camera model figure when appropriate since I think it provides a good overview of the pose estimation process with perspective camera.

Pull Request Readiness Checklist

See details at https://github.com/opencv/opencv/wiki/How_to_contribute#making-a-good-pull-request

• I agree to contribute to the project under Apache 2 License.
• To the best of my knowledge, the proposed patch is not based on a code under GPL or another license that is incompatible with OpenCV
• The PR is proposed to the proper branch
• There is a reference to the original bug report and related work
• There is accuracy test, performance test and test data in opencv_extra repository, if applicable
  Patch to opencv_extra has the same branch name.
• The feature is well documented and sample code can be built with the project CMake