"path" not a valid property for Image.source

I'm trying to change the background image set by xaml this way:

      <s:SurfaceWindow.Resources>
    <ImageBrush x:Key="WindowBackground" 
Stretch="None" Opacity="0.6" ImageSource="pack://application:,,,/Resources/img/bg/Default.jpg"/>
  </s:SurfaceWindow.Resources>

by using the following code in a method:

        sessionWindow.SetValue(ImageBrush.ImageSourceProperty, "..//..//Resources//im开发者_StackOverflowg//bg//Aqua.jpg");

where sessionWindow is the the actual window. It throws the exception in the title

The ImageBrush.ImageSource property is of type ImageSource.

Therefore, you need to set it to an ImageSource instance.
Also, your path is wrong.

For example:

sessionWindow.SetValue(ImageBrush.ImageSourceProperty,
     new BitmapImage(
        new Uri(@"..\..\Resources\img\bg\Aqua.jpg", UriKind.Relative)
     )
);

However, this won't actually change the background - Window doesn't have an ImageSource property.
Instead, you should set the Window's Background property, like this:

sessionWindow.Background = new ImageBrush {
     ImageSource = new BitmapImage(
        new Uri(@"..\..\Resources\img\bg\Aqua.jpg", UriKind.Relative)
     )
};