在WPF中使用MVVM拖动鼠标时绘制矩形

下面是我的xaml。我在画布中有一个图像。当鼠标在图像上拖动时，我想在图像上画一个矩形。我在WPF中成功做到了。但现在我想用MVVM来做。而不是在代码后面的事件处理程序，我想让他们在我的ViewModel。我使用MVVM基础实现MVVM。下面是MVVM基金会的链接。http://mvvmfoundation.codeplex.com/

非常感谢任何帮助。

XAML

<Canvas Name="cnvImage">
        <Image Height="348" HorizontalAlignment="Left" Margin="12,39,0,0" Name="imgPreview" 
               Stretch="Fill" VerticalAlignment="Top" Width="443" 
               Source="/Images/CapturedImage.png" 
                MouseDown="imgCamera_MouseDown" MouseMove="imgCamera_MouseMove" MouseUp="imgCamera_MouseUp" />
    </Canvas>

用

// This is the rectangle to be shown when mouse is dragged on camera image.
private Point startPoint;
private Rectangle rectSelectArea;

/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseDown(object sender, MouseButtonEventArgs e)
{
    startPoint = e.GetPosition(cnvImage);
    // Remove the drawn rectanglke if any.
    // At a time only one rectangle should be there
    if (rectSelectArea != null)
        cnvImage.Children.Remove(rectSelectArea);
    // Initialize the rectangle.
    // Set border color and width
    rectSelectArea = new Rectangle
    {
        Stroke = Brushes.LightBlue,
        StrokeThickness = 2
    };
    Canvas.SetLeft(rectSelectArea, startPoint.X);
    Canvas.SetTop(rectSelectArea, startPoint.X);
    cnvImage.Children.Add(rectSelectArea);
}
/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseMove(object sender, MouseEventArgs e)
{
    if (e.LeftButton == MouseButtonState.Released || rectSelectArea == null)
        return;
    var pos = e.GetPosition(cnvImage);
    // Set the position of rectangle
    var x = Math.Min(pos.X, startPoint.X);
    var y = Math.Min(pos.Y, startPoint.Y);
    // Set the dimenssion of the rectangle
    var w = Math.Max(pos.X, startPoint.X) - x;
    var h = Math.Max(pos.Y, startPoint.Y) - y;
    rectSelectArea.Width = w;
    rectSelectArea.Height = h;
    Canvas.SetLeft(rectSelectArea, x);
    Canvas.SetTop(rectSelectArea, y);
}
/// <summary>
/// 
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void imgCamera_MouseUp(object sender, MouseButtonEventArgs e)
{
    rectSelectArea = null;
}

我需要知道我需要在我的视图模型中写什么，以及相应地在XAML中需要做哪些更改。