Screen Capture, decrease bitmap file size

Question

One of the functions of the project that I am working makes the capture of the user screen, however the bitmap file is getting too big, from 6MB to 8MB, It is bad to be able to send via socket or future make a stream per frame, Could anyone help me in how I can decrease the size of this file? I’ll be posting the code I’m using to capture the screen, and then save it to a file..

    void Remote_Manip::CaptureScreen(Socket_Setup &socket_setup)
{
    int nScreenWidth = GetSystemMetrics(SM_CXSCREEN);
    int nScreenHeight = GetSystemMetrics(SM_CYSCREEN);
    HWND hDesktopWnd = GetDesktopWindow();
    HDC hDesktopDC = GetDC(hDesktopWnd);
    HDC hCaptureDC = CreateCompatibleDC(hDesktopDC);
    HBITMAP hCaptureBitmap = CreateCompatibleBitmap(hDesktopDC,
        nScreenWidth, nScreenHeight);
    SelectObject(hCaptureDC, hCaptureBitmap);
    BitBlt(hCaptureDC, 0, 0, nScreenWidth, nScreenHeight,
        hDesktopDC, 0, 0, SRCCOPY | CAPTUREBLT);

    WCHAR path[MAX_PATH];
    if (SUCCEEDED(SHGetFolderPathW(NULL, CSIDL_PROFILE, NULL, 0, path)))
    {
        std::wstring directory_create = path;
        std::string DEFAULT_DIR;

        DEFAULT_DIR.append(directory_create.begin(), directory_create.end());
        DEFAULT_DIR.append("\\Pictures");
        DEFAULT_DIR.append("\\image.bmp");

        LPCSTR fname = DEFAULT_DIR.c_str();
        HPALETTE hpal = NULL;
        saveBitmap(fname, hCaptureBitmap, hpal);

        ReleaseDC(hDesktopWnd, hDesktopDC);
        DeleteDC(hCaptureDC);
        DeleteObject(hCaptureBitmap);

        // fução para enviar a imagem via socket.
        FILE_DOWNLOAD(DEFAULT_DIR.c_str(), socket_setup);
    }
}