(delphi)print image problem

Here's what I use:

function PrintWrapper(ADrawProc : TDrawProc;
                      APreview: Boolean;
                      AWidth, AHeight : longint) : boolean;
var
  bmp : Graphics.TBitmap;
  PixPerInchX, PixPerInchY : longint;
begin
  bmp := Graphics.TBitmap.Create;
  try
    if APreview then begin
      PixPerInchX := GetDeviceCaps(bmp.Canvas.Handle, LOGPIXELSX);
      PixPerInchY := GetDeviceCaps(bmp.Canvas.Handle, LOGPIXELSY);
      bmp.Width := PixPerInchX * AWidth;
      bmp.Height := PixPerInchY * AHeight;
      bmp.Canvas.Brush.Color := clWhite;
      bmp.Canvas.FillRect(Rect(0,0,bmp.Width,bmp.Height));
      ADrawProc(bmp.Canvas,AWidth,AHeight);
      result := (not APreview) or TFormImagePrintPreview.PrintNow(bmp);
      if not result then
        exit;
    end;
    Printer.Orientation := poLandscape;
    Printer.BeginDoc;
    try
      ADrawProc(Printer.Canvas,AValues,AWidth,AHeight);
    finally
      Printer.EndDoc;
    end;
    result := true;
  finally
    FreeAndNil(bmp);
  end;
end;

Where DrawProc is:

type
  TDrawProc = procedure(ACanvas : TCanvas;
                        Width, Height : longint);

And the image preview is:

unit formImagePreviewDef;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls;

type
  TformImagePrintPreview = class(TForm)
    pnBottom: TPanel;
    btPrint: TButton;
    btCancel: TButton;
    imgMain: TImage;
    lbNotes: TLabel;
    procedure btPrintClick(Sender: TObject);
    procedure btCancelClick(Sender: TObject);
  public
    procedure Init(AGraphic : TGraphic; ANotes : string = '');
    class function  PrintNow(AGraphic : TGraphic; ANotes : string = '') : boolean;
  end;

implementation

{$R *.dfm}

{ TformImagePrintPreview }

procedure TformImagePrintPreview.btCancelClick(Sender: TObject);
begin
  Close;
  ModalResult := mrCancel;
end;

procedure TformImagePrintPreview.btPrintClick(Sender: TObject);
begin
  Close;
  ModalResult := mrOk;
end;

procedure TformImagePrintPreview.Init(AGraphic: TGraphic; ANotes : string = '');
const
  MAXSIZE = 600;
begin
  lbNotes.caption := ANotes;
  imgMain.Picture.Assign(AGraphic);
  if AGraphic.Height > AGraphic.Width then begin
    ClientWidth := trunc(MAXSIZE * AGraphic.Width / AGraphic.Height);
    ClientHeight := MAXSIZE + pnBottom.Height;
  end else begin
    Width := MAXSIZE;
    Height := trunc(MAXSIZE * AGraphic.Height/ AGraphic.Width)+pnBottom.Height;
  end;
end;

class function TformImagePrintPreview.PrintNow(AGraphic: TGraphic; ANotes : string = ''): boolean;
var
  form : TformImagePrintPreview;
begin
  form := TformImagePrintPreview.Create(nil);
  try
    form.Init(AGraphic,ANotes);
    result := form.ShowModal = mrOk;
  finally
    FreeAndNil(form);
  end;
end;

end.

Perhaps you ignore the fact that the printing page has different resolution from a screen page.
The points you want to draw on the printing canvas should be multiplied by a factor, like Zartog uses in his example:

  PixPerInchX := GetDeviceCaps(bmp.Canvas.Handle, LOGPIXELSX);
  PixPerInchY := GetDeviceCaps(bmp.Canvas.Handle, LOGPIXELSY);
  bmp.Width := PixPerInchX * AWidth;
  bmp.Height := PixPerInchY * AHeight;

Here is a simple tutorial on how to print: Printing Directly from Delphi