TCircleImage

type
  TCircleImage = class(TCustomControl)
    protected
      procedure Paint; override;
    public
      constructor Create(AOwner: TComponent); override;
  end;

type
  TForm1 = class(TForm)
    Image1: TImage;
    procedure CircleImageMouseDown(Sender: TObject; Button: TMouseButton;
      Shift: TShiftState; X, Y: Integer);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  CircleImage: TCircleImage;

implementation

{$R *.DFM}

constructor TCircleImage.Create(AOwner: TComponent);
begin
  inherited Create(AOwner);
  Width:= 100;
  Height:= 100;
end;

procedure TCircleImage.Paint;
var aRect: TRect;
begin
  aRect:= Rect(0, 0, 100, 100);
  Canvas.CopyRect(aRect, Form1.Image1.Canvas, aRect);
end;

procedure TForm1.CircleImageMouseDown(Sender: TObject; Button: TMouseButton;
  Shift: TShiftState; X, Y: Integer);
var aHandle: THandle;
begin
  aHandle:= (Sender as TCircleImage).Handle;
  BringWindowToTop(aHandle);
  ReleaseCapture;
  SendMessage(aHandle, WM_NCLBUTTONDOWN, 2, 0);    // 2 = HTCAPTION
end;

procedure TForm1.FormCreate(Sender: TObject);
begin
  CircleImage:= TCircleImage.Create(Self);
  CircleImage.Parent:= Self;
  SetWindowRgn(CircleImage.Handle, CreateEllipticRgn(0, 0, 100, 100), true);
  CircleImage.OnMouseDown:= CircleImageMouseDown;
  CircleImage.Left:= 10;
  CircleImage.Top:= 10;
end;