Use the TransformedBitmap element to rotate an image.
[XAML]
<Image Width='200' Height='200'>
<Image.Source>
<TransformedBitmap Source='C:\Documents and Settings\All Users\Documents\My Pictures\Sample Pictures\Winter.jpg'>
<TransformedBitmap.Transform>
<RotateTransform Angle='270' />
</TransformedBitmap.Transform>
</TransformedBitmap>
</Image.Source>
</Image>
Share with