With the Opacity Mask : ImageBrush « Windows Presentation Foundation « VB.Net Tutorial

1. VB.Net Tutorial
2. Windows Presentation Foundation
3. ImageBrush

<Window  
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    x:Class="SDKSample.SampleViewer"
    Title="Examples" >

   <Canvas> 
      <Image Height="150" Width="200" Source="c:\image.jpg" HorizontalAlignment="Left" Margin="10">
        <Image.OpacityMask>
          <ImageBrush Viewport="0,0,50,50" ViewportUnits="Absolute"
            TileMode="Tile" ImageSource="c:\image.png"/>
        </Image.OpacityMask>
      </Image>
   </Canvas> 
</Window>

16.79.ImageBrush
	16.79.1.	ImageBrush Examples
	16.79.2.	ImageBrush TileMode='Tile'
	16.79.3.	ImageBrush TileMode='FlipX'
	16.79.4.	ImageBrush TileMode='FlipY'
	16.79.5.	ImageBrush TileMode='FlipXY'
	16.79.6.	The ImageBrush's content is vertically aligned with the top of the output area.
	16.79.7.	The ImageBrush's content is vertically centered
	16.79.8.	The ImageBrush's content is vertically aligned with the bottom of the output area
	16.79.9.	The ImageBrush's content is right-aligned
	16.79.10.	The ImageBrush's content is left-aligned
	16.79.11.	The ImageBrush's content is centered horizontally
	16.79.12.	With the Opacity Mask
	16.79.13.	Use an ImageBrush to paint an area with an image
	16.79.14.	None Stretch ImageBrush
	16.79.15.	Uniform Stretch ImageBrush
	16.79.16.	The ImageBrush's content is not tiled in this example
	16.79.17.	The ImageBrush's content is tiled in this example
	16.79.18.	The ImageBrush's content is flipped horizontally as it is tiled
	16.79.19.	ImageBrush's content is not tiled
	16.79.20.	ImageBrush's tiles are set to 10% by 10% of the output area
	16.79.21.	ImageBrush's tiles are set to 10% by 30% of the output area
	16.79.22.	ImageBrush's tiles are set to 50% by 50% of the output area
	16.79.23.	ImageBrush's tiles are set to 25 by 25 pixels
	16.79.24.	ImageBrush's tiles are set to 25 by 50 pixels
	16.79.25.	ImageBrush ViewportUnits=Absolute
	16.79.26.	The ImageBrush has its Stretch property set to Uniform: the image is expanded as large as possible
	16.79.27.	ImageBrush has its Stretch property set to UniformToFill: image is expanded to completely fill the rectangle, but its aspect ratio is preserved
	16.79.28.	ImageBrush has its Stretch property set to Fill: image is expanded to completely fill the rectangle.
	16.79.29.	Text's Foreground = ImageBrush. The resulting text is filled with an image
	16.79.30.	Panel's Background property with an ImageBrush
	16.79.31.	The ImageBrush's content is flipped vertically as it is tiled
	16.79.32.	The ImageBrush's content is flipped horizontally and vertically as it is tiled
	16.79.33.	Fill rectangle with UniformToFill ImageBrush
	16.79.34.	Fill Polygon with Left aligned Uniform ImageBrush
	16.79.35.	RotateTransform ImageBrush.RelativeTransform
	16.79.36.	RotateTransform ImageBrush.Transform
	16.79.37.	Specifying a Stretch and a TileMode
	16.79.38.	Specifying a Stretch and alignment