uses
 Printers;
procedure TForm1.Button1Click(Sender: TObject);
var
 ScaleX, ScaleY: Integer;
 RR: TRect;
begin
 with Printer do
 begin
  BeginDoc;
  // The StartDoc function starts a print job.
  try
  ScaleX := GetDeviceCaps(Handle, logPixelsX) div PixelsPerInch;
  ScaleY := GetDeviceCaps(Handle, logPixelsY) div PixelsPerInch;
  // Retrieves information about the Pixels per Inch of the Printer.
  RR := Rect(0, 0, Image1.picture.Width * scaleX, Image1.Picture.Height * ScaleY);
  Canvas.StretchDraw(RR, Image1.Picture.Graphic);
  // Stretch to fit
  finally
  EndDoc;
  end;
 end;
end;

// Based on posting to borland.public.delphi.winapi by Rodney E Geraghty, 8/8/97.

procedure PrintBitmap(Canvas: TCanvas; DestRect: TRect; Bitmap: TBitmap);
var
 BitmapHeader: pBitmapInfo;
 BitmapImage: Pointer;
 HeaderSize: DWORD;
 ImageSize: DWORD;
begin
 GetDIBSizes(Bitmap.Handle, HeaderSize, ImageSize);
 GetMem(BitmapHeader, HeaderSize);
 GetMem(BitmapImage, ImageSize);
 try
  GetDIB(Bitmap.Handle, Bitmap.Palette, BitmapHeader^, BitmapImage^);
  StretchDIBits(Canvas.Handle,
  DestRect.Left, DestRect., // Destination Origin
  DestRect.Right - DestRect.Left, // Destination Width
  DestRect.Bottom - DestRect., // Destination Height
  0, 0, // Source Origin
  Bitmap.Width, Bitmap.Height, // Source Width & Height
  BitmapImage,
  TBitmapInfo(BitmapHeader^),
  DIB_RGB_COLORS,
  SRCCOPY)
 finally
  FreeMem(BitmapHeader);
  FreeMem(BitmapImage)
 end
end {PrintBitmap};

// from <a href="http://www.experts-exchange.com" title="www.experts-exchange.com">www.experts-exchange.com</a>
uses
 printers;
procedure DrawImage(Canvas: TCanvas; DestRect: TRect; ABitmap: TBitmap);
var
 Header, Bits: Pointer;
 HeaderSize: DWORD;
 BitsSize: DWORD;
begin
 GetDIBSizes(ABitmap.Handle, HeaderSize, BitsSize);
 Header := AllocMem(HeaderSize);
 Bits := AllocMem(BitsSize);
 try
  GetDIB(ABitmap.Handle, ABitmap.Palette, Header^, Bits^);
  StretchDIBits(Canvas.Handle, DestRect.Left, DestRect.,
  DestRect.Right, DestRect.Bottom,
  0, 0, ABitmap.Width, ABitmap.Height, Bits, TBitmapInfo(Header^),
  DIB_RGB_COLORS, SRCCOPY);
 finally
  FreeMem(Header, HeaderSize);
  FreeMem(Bits, BitsSize);
 end;
end;
procedure PrintImage(Image: TImage; ZoomPercent: Integer);
 // if ZoomPercent=100, Image will be printed across the whole page
var
 relHeight, relWidth: integer;
begin
 Screen.Cursor := crHourglass;
 Printer.BeginDoc;
 with Image.Picture.Bitmap do
 begin
  if ((Width / Height) > (Printer.PageWidth / Printer.PageHeight)) then
  begin
  // Stretch Bitmap to width of PrinterPage
  relWidth := Printer.PageWidth;
  relHeight := MulDiv(Height, Printer.PageWidth, Width);
  end
  else
  begin
  // Stretch Bitmap to height of PrinterPage
  relWidth := MulDiv(Width, Printer.PageHeight, Height);
  relHeight := Printer.PageHeight;
  end;
  relWidth := Round(relWidth * ZoomPercent / 100);
  relHeight := Round(relHeight * ZoomPercent / 100);
  DrawImage(Printer.Canvas, Rect(0, 0, relWidth, relHeight), Image.Picture.Bitmap);
 end;
 Printer.EndDoc;
 Screen.cursor := crDefault;
end;
// Example Call:
procedure TForm1.Button1Click(Sender: TObject);
begin
 // Print image at 40% zoom:
 PrintImage(Image1, 40);
end;