Simply wrap the Image in a Border control
<Border BorderThickness="1">
<Image Name="imgPic1"
Width="100"
Height="75"
Stretch="Fill"
VerticalAlignment="Top" />
</Border>
You could also provide a style you apply to images that does this if you don’t want to do it around every image
Final solution from answer and comments added by Pax:
<Border BorderThickness="1"
BorderBrush="#FF000000"
VerticalAlignment="Top">
<Image Name="imgPic1"
Width="100"
Height="75"
Stretch="Fill"
VerticalAlignment="Top"/>
</Border>