How to add a metric between two sets of points on a face so that it can be used to detect an object in digital images for face recognition

Question

How to add a metric between two sets of points on a face so that it can be used to detect an object in digital images for face recognition

I want to add a metric between two points on the face in order to use it to detect an object in digital images, we limit it to two dimensions, as shown below

I could recognize face functions as shown below using:

 -(void)markFaces:(UIImageView *)facePicture
 {
     // draw a CI image with the previously loaded face detection picture
     CIImage* image = [CIImage imageWithCGImage:facePicture.image.CGImage];

     // create a face detector - since speed is not an issue we'll use a high accuracy
     // detector
     CIDetector* detector = [CIDetector detectorOfType:CIDetectorTypeFace
                                          context:nil options:     [NSDictionary dictionaryWithObject:CIDetectorAccuracyHigh forKey:CIDetectorAccuracy]];

     // create an array containing all the detected faces from the detector
     NSArray* features = [detector featuresInImage:image];

     // we'll iterate through every detected face.  CIFaceFeature provides us
     // with the width for the entire face, and the coordinates of each eye
     // and the mouth if detected.  Also provided are BOOL for the eye and
     // mouth so we can check if they already exist.
     for(CIFaceFeature* faceFeature in features)
     {
         // get the width of the face
         CGFloat faceWidth = faceFeature.bounds.size.width;

         // create a UIView using the bounds of the face
         UIView* faceView = [[UIView alloc] initWithFrame:faceFeature.bounds];

         // add a border around the newly created UIView
         faceView.layer.borderWidth = 1;
         faceView.layer.borderColor = [[UIColor redColor] CGColor];

         // add the new view to create a box around the face
    [self.view addSubview:faceView];

         if(faceFeature.hasLeftEyePosition)
         {
             // create a UIView with a size based on the width of the face
             UIView* leftEyeView = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.leftEyePosition.x-faceWidth*0.15, faceFeature.leftEyePosition.y-faceWidth*0.15, faceWidth*0.3, faceWidth*0.3)];
             // change the background color of the eye view
             [leftEyeView setBackgroundColor:[[UIColor blueColor] colorWithAlphaComponent:0.3]];
             // set the position of the leftEyeView based on the face
             [leftEyeView setCenter:faceFeature.leftEyePosition];

           // round the corners
             leftEyeView.layer.cornerRadius = faceWidth*0.15;
             // add the view to the window
             [self.view addSubview:leftEyeView];
         }

         if(faceFeature.hasRightEyePosition)
         {
             // create a UIView with a size based on the width of the face
             UIView* leftEye = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.rightEyePosition.x-faceWidth*0.15, faceFeature.rightEyePosition.y-faceWidth*0.15, faceWidth*0.3, faceWidth*0.3)];
             // change the background color of the eye view
             [leftEye setBackgroundColor:[[UIColor blueColor] colorWithAlphaComponent:0.3]];
             // set the position of the rightEyeView based on the face
             [leftEye setCenter:faceFeature.rightEyePosition];
             // round the corners
             leftEye.layer.cornerRadius = faceWidth*0.15;
             // add the new view to the window
             [self.view addSubview:leftEye];
         }     

         if(faceFeature.hasMouthPosition)
         {
             // create a UIView with a size based on the width of the face
             UIView* mouth = [[UIView alloc] initWithFrame:CGRectMake(faceFeature.mouthPosition.x-faceWidth*0.2, faceFeature.mouthPosition.y-faceWidth*0.2, faceWidth*0.4, faceWidth*0.4)];
             // change the background color for the mouth to green
             [mouth setBackgroundColor:[[UIColor greenColor] colorWithAlphaComponent:0.3]];

             // set the position of the mouthView based on the face
             [mouth setCenter:faceFeature.mouthPosition];

              // round the corners
             mouth.layer.cornerRadius = faceWidth*0.2;

             // add the new view to the window
             [self.view addSubview:mouth];
              }
          }
      }

      -(void)faceDetector
      {
          // Load the picture for face detection
          //UIImageView* image = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"facedetectionpic.jpg"]];
          UIImageView* image = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"timthumb.png"]];
          // Draw the face detection image
          [self.view addSubview:image];

          // Execute the method used to markFaces in background
          [self performSelectorInBackground:@selector(markFaces:) withObject:image];

          // flip image on y-axis to match coordinate system used by core image
          [image setTransform:CGAffineTransformMakeScale(1, -1)];

          // flip the entire window to make everything right side up
          [self.view setTransform:CGAffineTransformMakeScale(1, -1)];


      }

Now I want to add points to find a link to the eyes, nose, etc. before uploading to the database. Later, these images can be compared with existing images based on this metric point location, as shown below.