.cs file:
  public class xxModel:PageModel {
  ...
  public string UploadImage(string imageName) {
       var image = elseware.GetImage(imageName);
       string newPath = saveImage(image);
       return newPath;
       }
  }

.cshtml file:

var pollForImage = function (imageName) {
  var imagePath = @Model.UploadImage(imageName); //<== this is where it
                                                 // fails.. I cannot get
                                                 // the call to work with
                                                 // a parameter..
  $("#image").attr("src", imagePath);
}