use Proportion to compare

after getting the key points, i come across a problem
 😭  Problem

   Because the size of the head in different pictures are not the same, Using the Length and Distance to compare the pictures is far from accurate.

💡 Solution!

   Proportion is used to help me get rid of this problem.

     How?

        Consider the iris_dist to be the base.

        So..... I get:

     eye_iris                = eye_length / iris_dist ;
         eyebrow_iris        = eyebrow_length / iris_dist;
 nose_iris              = nose_width / iris_dist ;
 mouth_iris            = mouth_length / iris_dist ;
   
         eye_dist_iris         = eye_dist / iris_dist ;
         nose_mouth_iris   = nose_mouth / iris_dist ;