I try to do this, but it doesn't work:
<Border
HorizontalAlignment="Stretch"
VerticalAlignment="Stretch">
<Border.Background>
<ImageBrush
AlignmentX="Left"
AlignmentY="Top"
Source="/Assets/background.png"
Stretch="None"
TileMode="Tile" />
</Border.Background>
</Border>
It feels like something else needs to be done for TileMode="Tile" to make It work. The markup above just displays one image in the corner of the border and that's it.