Further to my previous question, which did not get a useful answer despite a bounty, I will try rephrasing the question.

Basically, when the user clicks the ellipsis in the object inspector, Delphi opens a file/open dialog. I want to replace this handling with my own, so that I can save the image's path.

I would have expected that all I need to do is to derive a class from TImage and override the Assign() function, as in the following code. However, when I do the assign function is never called. So, it looks like I need to override something else, but what?

unit my_Image;


interface

uses
  Classes, ExtCtrls, Jpeg, Graphics;

type
  Tmy_Image = class(Timage)
    private
      FPicture : TPicture;

    protected
      procedure OnChange(Sender: TObject);

    public { Public declarations }
      Constructor Create(AOwner: TComponent); override;  
      procedure   SetPicture(picture : TPicture); 
      procedure   Assign(Source: TPersistent); override;

    published  { Published declarations - available in the Object Inspector at design-time }
      property Picture : TPicture read FPicture write SetPicture;
  end;  // of class Tmy_Image()

  procedure Register;

implementation

uses Controls, Dialogs;

  procedure Register;
  begin
    RegisterComponents('Standard', [Tmy_Image]);
  end;

  Constructor Tmy_Image.Create(AOwner: TComponent);
  begin
    inherited;  // Call the parent Create method
    Hint := 'Add an image from a file|Add an image from a file'; // Tooltip | status bar text
    AutoSize := True;  // Control resizes when contents change (new image is loaded)
    Height := 104;
    Width  := 104;
    FPicture := TPicture.Create();
    self.Picture.Bitmap.LoadFromResourceName(hInstance, 'picture_poperty_bmp');
  end;

  procedure Tmy_Image.OnChange(Sender: TObject);
  begin
    Constraints.MaxHeight := Picture.Height;
    Constraints.MaxWidth  := Picture.Width;
    Self.Height := Picture.Height;
    Self.Width  := Picture.Width;
  end;

  procedure   Tmy_Image.SetPicture(picture : TPicture);
  begin
    MessageDlg('Tmy_Image.SetPicture', mtWarning, [mbOK], 0);   // never called
  end;


  procedure Tmy_Image.Assign(Source: TPersistent);
  begin
    MessageDlg('Tmy_Image.Assign', mtWarning, [mbOK], 0);   // never called
  end;

end.