Dim TargetImg As New System.Drawing.Bitmap(MyBase.Size.Width, MyBase.Size.Height)
MyBase.DrawToBitmap(TargetImg, New System.Drawing.Rectangle(0, 0, MyBase.Size.Width, MyBase.Size.Height))

System.Drawing.Bitmap TargetImg = new System.Drawing.Bitmap(base.Size.Width, base.Size.Height);
base.DrawToBitmap(TargetImg, new System.Drawing.Rectangle(0, 0, base.Size.Width, base.Size.Height));

private const int WM_PRINT = 0x0317;
private const int PRF_CLIENT = 0x00000004;
private const int PRF_CHILDREN = 0x00000010;

public Bitmap PrintWindowEx()
{
   Bitmap bmp = null;
   Graphics gr = null;
   IntPtr hdc = IntPtr.Zero;
   try
   {
      bmp = new Bitmap(this.ClientRectangle.Width, this.ClientRectangle.Height, this.CreateGraphics());
      gr = Graphics.FromImage(bmp);
      hdc = gr.GetHdc();
      IntPtr wParam = hdc;
      IntPtr lParam = new IntPtr(PRF_CLIENT | PRF_CHILDREN);
      Message msg = Message.Create(this.Handle, WM_PRINT, wParam, lParam);
      this.WndProc(ref msg);
      }
      catch { }
      finally
      {
         if (gr != null)
         {
            if (hdc != IntPtr.Zero)
               gr.ReleaseHdc(hdc);
            gr.Dispose();
         }
      }
   return bmp;
}

Procedure Make_Shoot(aForm : TForm; aBmp : TBitmap);
Var aDc : HDC;
Begin
  If (aForm = Nil) or (aBmp = Nil) Then Exit;
  With aBmp do
  Begin
    Height := aForm.Height;
    Width  := aForm.Width;
    aDC    := GetWindowDC(aForm.Handle);
    BitBlt(Canvas.Handle, 0, 0, Width, Height, aDC,
      0, 0, srcCopy);
    ReleaseDC(aForm.Handle, aDC);
  End;
End;

// Utilisation
procedure TfrmMain.btn_ShootClick(Sender: TObject);
Var Bmp : TBitmap;
begin
  Bmp := TBitmap.Create;
  Make_Shoot(Self, Bmp);
  // ... ici votre code pour enregistrer où afficher l'image ...
  Bmp.Free;
end;

// Une fonction place le contenu de la fenêtre en cours sous 
// forme graphique dans un champ image
dCopieImage(copieEcran,MonImage)
// Il est alors possible de conserver l'image sur disque
dSauveImageJPEG(MonImage, "C:\Temp\Image.jpg")

Private Const WM_PRINT As Integer = &H317
Private Const PRF_CLIENT As Integer = &H4
Private Const PRF_CHILDREN As Integer = &H10
Public Function PrintControl(ByVal Ctrl As System.Windows.Forms.Control) As System.Drawing.Bitmap
  Dim bmp As System.Drawing.Bitmap = Nothing
  Dim gr As System.Drawing.Graphics = Nothing
  Dim hdc As IntPtr = IntPtr.Zero
  Try
    bmp = New System.Drawing.Bitmap(Ctrl.ClientRectangle.Width, Ctrl.ClientRectangle.Height, Ctrl.CreateGraphics())
    gr = Graphics.FromImage(bmp)
    hdc = gr.GetHdc()
    Dim wParam As IntPtr = hdc
    Dim lParam As IntPtr = New IntPtr(PRF_CLIENT Or PRF_CHILDREN)
    Dim msg As System.Windows.Forms.Message = System.Windows.Forms.Message.Create(Ctrl.Handle, WM_PRINT, wParam, lParam)
    MyBase.WndProc(msg)
  Catch
  Finally
    If Not gr Is Nothing Then
      If hdc <> IntPtr.Zero Then gr.ReleaseHdc(hdc)
      gr.Dispose()
    End If
  End Try
  Return bmp
End Function

Private Declare Function PrintWindow Lib "user32" (ByVal hWnd As Long, ByVal hdcBlt As Long, ByVal nFlags As Long) As Long

PrintWindow Form1.hWnd, DestinationDC, 0

Function PrintWindow(ahwnd:HWND; hdcBlt:HDC;  nFlags:UINT): Bool; Stdcall; External 'User32.dll'  name 'PrintWindow'; 
Implementation 
Uses testwnd; { juste pour tester le code } 
{$R *.dfm} 
  // Prend un  instantané du hwnd de la fenêtre, 
  //  stocké dans le contexte de périphérique hdcMem de la mémoire  
  // cette méthode fonctionne même si la fenêtre  n'est pas 
  // en avant plan ou se trouve  en dehors de la zone écran 
Function  GetFullWindowImage(aHandle : THandle):TBitmap; 
Var DC, hdcMem : HDC; 
    aRect : TRect;  
    hBMP : HBitmap; 
    aWidth, aHeight : Integer; 
Begin 
  Result := Nil; 
  dc := GetWindowDC(0); 
  If (dc >  0) Then 
  Try  
    hdcMem := CreateCompatibleDC(dc); 
    If (hdcMem > 0) Then 
    Try 
      GetWindowRect(aHandle,  aRect); 
      aWidth := aRect.Right-aRect.Left; 
      aHeight :=  aRect.Bottom-aRect.Top; 
      hBMP := CreateCompatibleBitmap(dc, aWidth,  aHeight); 
      If (hBMP > 0) Then 
      Try  
        SelectObject(hdcMem, hBMP);  
        PrintWindow(aHandle, hdcMem, 0);  
        Result := TBitmap.Create; 
        Result.Width := aWidth;  
        Result.Height := aHeight; 
        BitBlt(Result.Canvas.Handle,  0, 0, aWidth, aHeight,  hdcMem, 0, 0, srcCopy);  
      Finally  
        DeleteObject(hBMP); 
      End; 
    Finally  
      DeleteObject(hdcMem); 
    End; 
  Finally  
    ReleaseDC(0, dc); 
  End; 
End;  
{ exemple d'utilisation} 
Procedure TForm1.Button3Click(Sender: TObject);  
Var FormImage : TBitmap; 
Begin 
  FormImage :=  GetFullWindowImage(testfrm.Handle); 
  Try  
    Image1.Picture.Bitmap.Assign(FormImage); 
  Finally 
    FormImage.Free; 
  End; 
End;