添加引用：uses JPEG;

//=====================图片处理函数，将覆盖原图片文件===========================
//=====filename:图片完整路径  PressQuality:压缩质量 Width:宽  Height:高
function CompressMainFun(filename: String; PressQuality,Width,Height:integer): Boolean;
var
  bmp: TBitmap;
  jpg: TJpegImage;
  i: Integer;
  sTemp:string;
begin
  Result := False;
    if pos(UpperCase('.bmp'), UpperCase(filename)) <> 0 then   //bmp格式
    begin
      bmp.LoadFromFile(filename);
      jpg.Assign(bmp);
      jpg.CompressionQuality := PressQuality;
      jpg.Compress;
      bmp.height := Height;
      bmp.Width := Width;
      bmp.Canvas.StretchDraw(bmp.Canvas.ClipRect, jpg);
      jpg.Assign(bmp);
      sTemp := filename + '.jpg';
      jpg.SaveToFile(sTemp);
      DeleteFile(filename);
      CopyFile(PChar(sTemp), PChar(filename), True);
      DeleteFile(sTemp);
    end
    else                                                     //其它格式
    begin
      jpg.LoadFromFile(filename);
      bmp.height := Height;
      bmp.Width := Width;
      bmp.Canvas.StretchDraw(bmp.Canvas.ClipRect, jpg);
      jpg.Assign(bmp);
      jpg.CompressionQuality := PressQuality;
      jpg.Compress;
      sTemp := filename + '.jpg';
      jpg.SaveToFile(sTemp);
      DeleteFile(filename);
      CopyFile(PChar(sTemp), PChar(filename), True);
      DeleteFile(sTemp);
    end;
  Result := True;
end;