unit foo;

interface

uses { a lot of units } ;

type
  TForm1 = class(TForm)
    // ... various components and other stuff from the form designer
    // one might be:
    procedure btnNewImageClick(Sender: TObject);
  private
    // private members go here
  public
    // public members go here
    // our event handler will be a public member procedure of the TForm1 class
    procedure FlipBitmapRight(Sender: TObject);
  end;

var
  Form1: TForm1;

implementation

// ... other event handlers and stuff go here

procedure TForm1.btnNewImageClick(Sender: TObject);
begin
  with TImage.Create(self) do
    try
      OnClick := FlipBitmapRight;
      Picture.LoadFromFile('test.bmp'); // or however it is...
    except
      Free;
    end;
end;

procedure TForm1.FlipBitmapRight(Sender: TObject);
var
  ClickedImage: TImage;
begin
  ClickedImage := Sender as TImage;
  // now do something with the image
end;

end.