在用VideoCaptureElement的过程中，不知道怎么获得摄像头的截图，纠结了整整一天，
最终在下面的网站上找到了答案，哈哈。（困的都不清醒的大脑，让我耐下心来看英文，上天还是很优待我的）
例子截图：
XAML：
<Window x:Class="Fish.AccountBook.View.Test.CameraWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="CameraWindow" Height="200" Width="300"
xmlns:WPFMediaKit="clr-namespace:WPFMediaKit.DirectShow.Controls;assembly=WPFMediaKit">
<Grid>
<Grid.RowDefinitions>
<RowDefinition Height="30" />
<RowDefinition Height="auto" />
</Grid.RowDefinitions>
<StackPanel Orientation="Horizontal">
<Button Name="button1" Content="截图" Height="23" Width="75" Click="button1_Click" />
</StackPanel>
<WPFMediaKit:VideoCaptureElement x:Name="m_VideoCaptureElement" Grid.Row="1" />
</Grid>
</Window>
CS：
public partial class CameraWindow : Window
{
public CameraWindow()
{
InitializeComponent(); string[] inputNames = MultimediaUtil.VideoInputNames;
m_VideoCaptureElement.VideoCaptureSource = inputNames[0];
} private void button1_Click(object sender, RoutedEventArgs e)
{
RenderTargetBitmap bmp = new RenderTargetBitmap((int)m_VideoCaptureElement.ActualWidth, (int)m_VideoCaptureElement.ActualHeight, 96, 96, PixelFormats.Rgb24);
bmp.Render(m_VideoCaptureElement);
BitmapEncoder encoder = new JpegBitmapEncoder();
encoder.Frames.Add(BitmapFrame.Create(bmp));
string now = DateTime.Now.Year + "" + DateTime.Now.Month + "" + DateTime.Now.Day + "" + DateTime.Now.Hour + "" + DateTime.Now.Minute + "" + DateTime.Now.Second;
string filename = "D:\\" + now + "pic.jpg";
FileStream fstream = new FileStream(filename, FileMode.Create);
encoder.Save(fstream);
fstream.Close(); }
}