How can I add watermark text to a textbox in wpf?

Question

Im working on a wpf application.How I can add watermark text to the textbox and passwordbox?

<Window x:Class="WpfApplication1.MainWindow"
   xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
   xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
   Title="Platforma Smart School 1.0" Height="580" Width="880" 
   Icon="/WpfApplication4;component/Images/capturennnnnn12_256px%20%282%291.ico">

<Grid>

    <Grid.Background>
       <ImageBrush ImageSource="/WpfApplication1;component/Images/
       hp-colorful-books-hd-105609.jpg" />
    </Grid.Background>

    <Rectangle Height="334" HorizontalAlignment="Left" Margin="608,162,0,0" 
    Name="rectangle1" Stroke="#FFDBD8D8" VerticalAlignment="Top" Width="222"
    Fill="#FFF0F0F0" />

    <Button Height="34" HorizontalAlignment="Left" Margin="630,434,0,0"
    Name="button1" VerticalAlignment="Top" Width="178" FontSize="13" 
    Foreground="#FF555555" />

    <TextBox Height="34" HorizontalAlignment="Left" Margin="630,219,0,0" 
    Name="textBox1" VerticalAlignment="Top" Width="178" FontSize="14" Text=""
    Foreground="#FF7C7A7A"  />

    <PasswordBox Height="32" HorizontalAlignment="Left" Margin="630,304,0,0"
    Name="passwordBox1" VerticalAlignment="Top" Width="178" FontSize="14"
    FontFamily="Segoe UI"/>

    <Image Height="134" HorizontalAlignment="Left" Margin="606,12,0,0" 
    Name="image1" Stretch="Fill" VerticalAlignment="Top" Width="224"
    Source="/WpfApplication1;component/Images/Capture3.PNG" />

    <Label Content=" Smart School" Height="31" HorizontalAlignment="Left" 
    Margin="251,498,0,0" Name="label1" VerticalAlignment="Top" Width="227" />

</Grid>

Answer 1

Take a look at this SO Question. The second answer of creating an Attached Property is what I would suggest.

There are also some extended WPF controls that can help: http://wpftoolkit.codeplex.com/wikipage?title=WatermarkTextBox

Edit: Added Extended WPF Toolkit link.