{.......}
type
  TImageContro = class(TWinControl)
  private
    fImage: TImage;
  protected
    procedure WndProc(var Message: TMessage); override; {HERE is the cause I tink... See implementation...}
  published
    constructor Create(AOwner: TComponent); override;
    destructor Destroy; override;

    property Image: TImage read fImage;    
  end;
{.......}

implementation
{.......}

constructor TImageControl.Create(AOwner: TComponent);
begin
  inherited Create(aOwner);
  Width := 100;
  Height := 100;
  fImage := TImage.Create(self);
  fImage.Align := alClient;
end;

destructor TImageControl.Destroy;
begin
  fImage.Free;
  inherited;
end;

procedure TImageControl.WndProc(var Message: TMessage);
var
  ps: TPaintStruct;
  DrawDC: HDC;
  brush: HBRUSH;
begin
  { WM_PAINT обрабатывается для того чтобы рисовать что-то в котроле пока не загрузили картинку.
    А вто только как проверить загружена ли эта картинка??? }
  if Message.Msg = WM_PAINT then
  begin
     DrawDC := BeginPaint(Handle, ps);
     brush := CreateHatchBrush(hs_Cross, clOlive);
     FillRect(DrawDC, ClientRect, brush);
     DeleteObject(brush);
     EndPaint(Handle, ps);
     Message.Result := 0;
     exit;
  end
  else
     inherited;
end;
{.......}

N>Как-то нехорошо при WM_PAINT-е каждый раз пытаться сохранять в файл

constructor TImageControl.Create(AOwner: TComponent);
begin
  inherited Create(aOwner);
  Width := 100;
  Height := 100;
  fImage := TImage.Create(self);
  fImage.Align := alClient;
  fImage.Visible := True; // где-то такое мне приходилось втыкать, по умолчанию создавался невидимый контрол
end;

unit ImageWinControl;

interface

uses
        Windows, Messages, SysUtils, Classes, Controls, ExtCtrls;

type
        TImageWinControl = class (TWinControl)
        private
                mImage : TImage;
                procedure mSetImage (image : TImage);
                procedure imageChanged (Sender : TObject);
        protected
        public
                constructor Create (owner : TComponent); override;
        published
                property Image : TImage read mImage write mSetImage;
        end;

procedure Register;

implementation

procedure TImageWinControl.mSetImage (image : TImage);
begin
        if Assigned (image) then
        begin
                mImage.Assign (image);
                mImage.Picture.OnChange := imageChanged;
        end;
end;

procedure TImageWinControl.imageChanged (Sender : TObject);
begin
        Refresh;
end;

constructor TImageWinControl.Create (owner : TComponent);
begin
        inherited;
        mImage := TImage.Create (Self);
        InsertControl (mImage);
        mImage.Visible := true;
        mImage.Align := alClient;
        mImage.Picture.OnChange := imageChanged;
end;

procedure Register;
begin
        RegisterComponents ('ImageWinControl', [TImageWinControl]);
end;

end.

С>procedure TImageWinControl.mSetImage (image : TImage);
С>begin
С>        if Assigned (image) then
С>        begin
С>                mImage.Assign (image);
С>                mImage.Picture.OnChange := imageChanged;
С>        end;
С>end;
С>

  if mImage.Picture.Width = 0 then
  begin
    //....
  end
  else
  begin
    //....
  end;