Is it possible to call a method once per frame inside of another method?

I'm working with live video processing.

My problem is that I want to call a method and inside this method I want to have a loop that runs every frame just like Update() but after a defined time I want to break the loop and return something.

I know that there is a while loop but as far as I know, this loop does everything in just one frame and that's not quite what I'm searching for.

Does anybody have a solution? I added a small example (not real code) to clarify what I mean.

 public void DetectFace()
     {
         int detectedFaces = 0;
         Vector2 nosePos;
 
         //loop that calls once a frame, I used while for demonstration
         while (detectedFaces < 10)
             if (FindFace())
             {
                 detectedFaces++;
                 nosePos = GetNosePos();
             }
             else
             {
                 detectedFaces = 0;
             }
 
         return nosePos;
     }