I suggest you to use a Binding on your imgGravatar from XAML. Set IsAsync=true on it and WPF will automatically utilize a thread from the thread pool to pull your image. You could encapsulate the resolving logic into an IValueConverter and simply bind the email as Source
in XAML:
<Window.Resouces>
<local:ImgConverter x:Key="imgConverter" />
</Window.Resource>
...
<Image x:Name="imgGravatar"
Source="{Binding Path=Email,
Converter={StaticResource imgConverter},
IsAsync=true}" />
in Code:
public class ImgConverter : IValueConverter
{
public override object Convert(object value, ...)
{
if (value != null)
{
BitmapImage bi = new BitmapImage();
bi.BeginInit();
bi.UriSource = new Uri(
GravatarImage.GetURL(
"http://www.gravatar.com/avatar.php?gravatar_id=" +
value.ToString()) , UriKind.Absolute
);
bi.EndInit();
return bi;
}
else
{
return null;
}
}
}