<xctk:WatermarkTextBox Watermark="Enter First Name" />

<xctk:WatermarkTextBox>
    <xctk:WatermarkTextBox.Watermark>
        <StackPanel Orientation="Horizontal">
            <Image Source="Contact16.png" Stretch="None" />
            <TextBlock Text="Enter First Name" Margin="4,0,0,0" />
        </StackPanel>
    </xctk:WatermarkTextBox.Watermark>
</xctk:WatermarkTextBox>

<xctk:WatermarkTextBox Watermark="Enter First Name">
    <xctk:WatermarkTextBox.WatermarkTemplate>
        <DataTemplate>
            <Border BorderBrush="Green" BorderThickness="1">
                <ContentControl Content="{Binding}" Foreground="DarkRed" FontWeight="Bold" Focusable="False" />
            </Border>
        </DataTemplate>
    </xctk:WatermarkTextBox.WatermarkTemplate>
</xctk:WatermarkTextBox>