[acertij022]

1º ante todo te pido disculpa por no leer tu pos seoane porque es la solucion.
Lo que no me sale ahora es redibujar la porción de BMP en el cliente

en servidor (que se le entrega al cliente) use el siguiente codigo:

Código Delphi [-]
unit Umain;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, StdCtrls, ExtCtrls, Jpeg, ZipForge, ScktComp, IdBaseComponent,
  IdComponent, IdTCPConnection, IdTCPClient;

type
  TFMain = class(TForm)
    Button1: TButton;
    MainZip: TZipForge; // componente para zipera y dezipear
    IdTCPClient1: TIdTCPClient;
    procedure GetDesktop();
    procedure comparar();
    procedure FormCreate(Sender: TObject);
    procedure Enviar(var streamZip:TStream);
    procedure Button1Click(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  FMain: TFMain;
  Recuadro : array [0..1000] of Trect;
  BMPEstado:integer=0; //indica que imagen esta para comparar
  Bitmap1,Bitmap2: TBitmap;
  StreamZip: TStream;
implementation

{$R *.dfm}
//##############################################################################
function Min(i,j: Integer): Integer;
begin
  if i < j then
    Result:= i
  else
    Result:= j;
end;
//##############################################################################
function Max(i,j: Integer): Integer;
begin
  if i > j then
    Result:= i
  else
    Result:= j;
end;
//##############################################################################
function Seleccionar(Bitmap_a, Bitmap_b: TBitmap):integer;
var
  P1, P2: PByte;
  a,b,i, j: Integer;
  R: TRect;
  intR:integer;
begin
  Result:=0;
  intR:=0;
  b:=0;
  R.Right:= 0;
  R.Bottom:= 0;
  R.Left:= Min(Bitmap_a.Width,Bitmap_b.Width);
  R.Top:= Min(Bitmap_a.Height,Bitmap_b.Height);
  Bitmap_a.PixelFormat:= pf24bit;
  Bitmap_b.PixelFormat:= pf24bit;
  for j:= 0 to Min(Bitmap_a.Height,Bitmap_b.Height) - 1 do
  begin
    a:=0;
    P1:= Bitmap_a.ScanLine[j];
    P2:= Bitmap_b.ScanLine[j];
    for i:= 0 to Min(Bitmap_a.Width,Bitmap_b.Width) - 1 do
    begin
      if not CompareMem(P1,P2,3) then
      begin
        R.Right:= Max(i,R.Right);
        R.Bottom:= Max(j,R.Bottom);
        R.Left:= Min(i,R.Left);
        R.Top:= Min(j,R.Top);
        a:=1;
        b:=1;
      end;
      inc(P1,3); inc(P2,3);
    end;
    if (a=0)and(b=1)then
        begin
        a:=0;b:=0;
        Recuadro[intR].Right :=R.Right;
        Recuadro[intR].Bottom:=R.Bottom;
        Recuadro[intR].Left  :=R.Left;
        Recuadro[intR].Top   :=R.Top;
        inc(intR);

        R.Right:= 0;
        R.Bottom:= 0;
        R.Left:= Min(Bitmap_a.Width,Bitmap_b.Width);
        R.Top:= Min(Bitmap_a.Height,Bitmap_b.Height);
        end;
  end;
  Result:=intR;
end;
//##############################################################################
procedure TFMain.comparar();
var
  desktop: TCanvas;
  Bitmap: TBitmap;
  int1,int2:integer;
  jpg: TJpegImage;
  stream: TStream;
  str1:string;
begin
  int2:=-1;
  Bitmap:= TBitmap.Create;
  jpg:=TJPegImage.Create;
//  MainZip.FileName:='data.zip';
  StreamZip:=TMemoryStream.Create;
  MainZip.OpenArchive(StreamZip,true);

  desktop:=TCanvas.Create;
  with DeskTop do Handle := GetWindowDC (GetDesktopWindow) ;

  try
    // Encontramos el recuadro donde estan localizados los cambios
    if BMPEstado=0 then int2:=0;
    if BMPEstado=2 then int2:=Seleccionar(Bitmap1,Bitmap2);
    if BMPEstado=1 then int2:=Seleccionar(Bitmap2,Bitmap1);
    // Copiamos ese recuadro en un nuevo bitmap
    if int2 = -1 then exit;
    for int1:=0 to int2 do
      begin
      Bitmap.Width:= Recuadro[int1].Right - Recuadro[int1].Left;
      Bitmap.Height:= Recuadro[int1].Bottom - Recuadro[int1].Top;
      if BMPEstado=0 then
         begin
         Bitmap.Width:= screen.Width;
         Bitmap.Height:= screen.Height;
         with Bitmap do Canvas.CopyRect(Rect(0,0,Bitmap1.Width, Bitmap1.Height),Bitmap1.Canvas,Rect(0,0,Bitmap1.Width, Bitmap1.Height));
         Recuadro[int1].Left:=0;
         Recuadro[int1].Top:=0;
         Recuadro[int1].Right:=Bitmap.Width;
         Recuadro[int1].Bottom:=Bitmap.Height;
         end;
      if BMPEstado=1 then  with Bitmap do Canvas.CopyRect(Rect(0,0,Width,Height),Bitmap1.Canvas,Recuadro[int1]);
      if BMPEstado=2 then  with Bitmap do Canvas.CopyRect(Rect(0,0,Width,Height),Bitmap2.Canvas,Recuadro[int1]);
      str1:=str1+IntToStr(Recuadro[int1].Left)+';';
      str1:=str1+IntToStr(Recuadro[int1].Top)+';';
      str1:=str1+IntToStr(Recuadro[int1].Right)+';';
      str1:=str1+IntToStr(Recuadro[int1].Bottom)+';'+#10;
      // convierto a jpeg
      stream:=TMemoryStream.Create;
      jpg.Assign(Bitmap);
      jpg.CompressionQuality:=80; //Calidad del JPEG
      jpg.Compress;      //Comprimimos la imagen
      jpg.SaveToStream(stream);
      jpg.SaveToFile(IntToStr(int1)+'.jpg');
      stream.Position:=0;
      MainZip.AddFromStream(IntToStr(int1)+'.jpg',stream,0,stream.Size);
      Stream.Free;
      end;
  finally
    Bitmap.Free;
    jpg.Free;
    stream:=TMemoryStream.Create;
    Stream.WriteBuffer(Pointer(str1)^, Length(str1));
    MainZip.AddFromStream('Position.txt',stream,0,stream.Size);
    MainZip.CloseArchive;

    desktop.Free;
    if str1<>'' then
      begin
      StreamZip.Position:=0;
      Enviar(StreamZip);
      end;
    StreamZip.Free;
  end;
end;
//##############################################################################
procedure TFMain.GetDesktop();
label salto;
var
desktop: TCanvas;
begin
if BMPEstado in[0,2] then
   begin
   Bitmap1.Width:=screen.Width;
   Bitmap1.Height:=screen.Height;
   desktop:=TCanvas.Create;
   with DeskTop do Handle := GetWindowDC (GetDesktopWindow) ;
   with Bitmap1.Canvas do CopyRect (Rect (0, 0, screen.Width, screen.Height),DeskTop,Rect (0, 0, screen.Width, screen.Height));
   desktop.Free;
   if BMPEstado=0 then
      begin
      comparar;
      BMPEstado:=1;
      goto salto;
      end;
   BMPEstado:=1;
   comparar;
   goto salto;
   end;
if BMPEstado =1 then
   begin
   Bitmap2.Width:=screen.Width;
   Bitmap2.Height:=screen.Height;
   desktop:=TCanvas.Create;
   with DeskTop do Handle := GetWindowDC (GetDesktopWindow) ;
   with Bitmap2.Canvas do CopyRect (Rect (0, 0, screen.Width, screen.Height),DeskTop,Rect (0, 0, screen.Width, screen.Height));
   desktop.Free;
   BMPEstado:=2;
   comparar;
   goto salto;
   end;
salto:;
end;
//##############################################################################
procedure TFMain.FormCreate(Sender: TObject);
begin
  Bitmap1:= TBitmap.Create;
  Bitmap2:= TBitmap.Create;
end;
//##############################################################################
procedure TFMain.Enviar(var StreamZip:TStream);
begin
IdTCPClient1.Connect;
IdTCPClient1.OpenWriteBuffer;
IdTCPClient1.WriteStream(StreamZip);
IdTCPClient1.CloseWriteBuffer;
IdTCPClient1.Disconnect;
end;
//##############################################################################
procedure TFMain.Button1Click(Sender: TObject);
begin
GetDesktop; // EN REALIDAD ESTO DEVERIA ESTAR EN UN TIMER
end;
//##############################################################################
end.

Y en el cliente (osea mi PC )coloco este codigo:

Código Delphi [-]
unit Umain;

interface

uses
  Windows, Messages, SysUtils, Variants, Classes, Graphics, Controls, Forms,
  Dialogs, ScktComp, ExtCtrls, ZipForge, IdBaseComponent, IdComponent,
  IdTCPServer, StdCtrls, Jpeg;

type
  TForm1 = class(TForm)
    imgDesktop: TImage;
    MainZip: TZipForge; // componente para zipera y dezipear 
    IdTCPServer1: TIdTCPServer;
    procedure IdTCPServer1Execute(AThread: TIdPeerThread);
    procedure FormCreate(Sender: TObject);
  private
    { Private declarations }
  public
    { Public declarations }
  end;

var
  Form1: TForm1;
  Desktop1:TBitmap;

implementation

{$R *.dfm}
//##############################################################################
procedure TForm1.IdTCPServer1Execute(AThread: TIdPeerThread);
var
AStream,FileStream:TStream;
str1,strPosicion:string;
int1,int2:integer;
jpg: TJpegImage;
Bitmap1: TBitmap;
R:Trect;
begin
  with AThread.Connection do
  begin
  AStream:=TMemoryStream.Create;
  ReadStream(AStream, -1, true);
  AStream.Position:=0;
  MainZip.OpenArchive(AStream,false);
  MainZip.ExtractToString('Position.txt',str1);
  caption:=str1;
  int2:=0;
  while length(str1)>0 do
    begin
    if pos(#10,str1)>0 then
       begin
       strPosicion:=copy(str1,1,pos(#10,str1)-1);
       int1:=pos(';',strPosicion); R.Left:=StrToInt(copy(strPosicion,1,int1-1)); strPosicion:=copy(strPosicion,int1+1,length(strPosicion));
       int1:=pos(';',strPosicion); R.Top:=StrToInt(copy(strPosicion,1,int1-1)); strPosicion:=copy(strPosicion,int1+1,length(strPosicion));
       int1:=pos(';',strPosicion); R.Right:=StrToInt(copy(strPosicion,1,int1-1)); strPosicion:=copy(strPosicion,int1+1,length(strPosicion));
       int1:=pos(';',strPosicion); R.Bottom:=StrToInt(copy(strPosicion,1,int1-1)); strPosicion:=copy(strPosicion,int1+1,length(strPosicion));
       str1:=copy(str1,pos(#10,str1)+1,length(str1));
       FileStream:=TMemoryStream.Create;
       MainZip.ExtractToStream(IntToStr(int2)+'.jpg',FileStream);
       FileStream.Position:=0;
       jpg:=TJPegImage.Create;
       jpg.LoadFromStream(FileStream);
       FileStream.Free;
       Bitmap1:=TBitmap.Create;
       Bitmap1.Assign(jpg);
       if Desktop1.Widththen Desktop1.Width:=Bitmap1.Width;
       if Desktop1.Heightthen Desktop1.Height:=Bitmap1.Height;
       with Desktop1 do Canvas.CopyRect(R,Bitmap1.Canvas,R);//FUNCIONA LA 1º VEZ (PANTALLA COMPLETA)
       imgDesktop.Picture.Assign(Desktop1);
       Bitmap1.Free;
       jpg.Free;
       inc(int2);
       end;
    end;
  MainZip.CloseArchive;
  AStream.Free;
  end;
end;
//##############################################################################
procedure TForm1.FormCreate(Sender: TObject);
begin
Desktop1:=TBitmap.Create;
end;
//##############################################################################
end.

Como lo indique en el codigo solo me funciona una unica ves el copiar un BMP en una parte de otro BMP

Si a alguien sabe porque por favor me lo puden explicar o indicarme como solucionarlo.
Desde ya muchas gracias a todos por los aportes