截取屏幕，并保存为JPEG文件格式

 1 using jpeg,ExtCtrls;
 2 procedure TForm1.ScreenCap(LeftPos,TopPos,RightPos,BottomPos:integer);
 3 var
 4   RectWidth,RectHeight:integer;
 5   SourceDC,DestDC,Bhandle:integer;
 6   Bitmap:TBitmap;
 7   MyJpeg: TJpegImage;
 8   Stream:TMemoryStream;
 9 begin
10   MyJpeg:= TJpegImage.Create;
11   RectWidth:=RightPos-LeftPos;
12   RectHeight:=BottomPos-TopPos;
13   SourceDC:=CreateDC('DISPLAY','','',nil);
14   DestDC:=CreateCompatibleDC(SourceDC);
15   Bhandle:=CreateCompatibleBitmap(SourceDC,
16   RectWidth,RectHeight);
17   SelectObject(DestDC,Bhandle);
18   BitBlt(DestDC,0,0,RectWidth,RectHeight,SourceDC,
19   LeftPos,TopPos,SRCCOPY);
20   Bitmap:=TBitmap.Create;
21   Bitmap.Handle:=BHandle;
22   Stream := TMemoryStream.Create;
23   Bitmap.SaveToStream(Stream);
24   Stream.Free;
25   try
26     MyJpeg.Assign(Bitmap);
27     MyJpeg.CompressionQuality:=70;
28     MyJpeg.Compress;
29     MyJpeg.SaveToFile('C:\MyJPEGImage.JPG');
30   finally
31     MyJpeg.Free;
32     Bitmap.Free;
33     DeleteDC(DestDC);
34     ReleaseDC(Bhandle,SourceDC);
35   end;
36 end;