public class Settings : INotifyPropertyChanged
{
    public enum WatermarkType {None, Text, Image};

    public event PropertyChangedEventHandler PropertyChanged;
            private void NotifyPropertyChanged(String propertyName)
            {
                PropertyChangedEventHandler handler = PropertyChanged;
                if (null != handler)
                {
                    handler(this, new PropertyChangedEventArgs(propertyName));
                }
            }
    }

public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            string parameterString = parameter as string;

            Type temp = value.GetType();

            object parameterValue = Enum.Parse(value.GetType(), parameterString);

            return parameterValue.Equals(value);

        }

        public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            string parameterString = parameter as string;
           /* if (parameterString == null)
                return DependencyProperty.UnsetValue;*/

            return Enum.Parse(targetType, parameterString);
        }

<StackPanel Name="StackPanelWatermarkType"  Margin="10,0,0,0" Grid.Row="2">
                <RadioButton GroupName="waterMarkType" IsChecked="{Binding Path=watermarkType, Converter={StaticResource EnumConverter}, ConverterParameter=None}"
                                                        Name="rbtWatermarkNone" Checked="rbtWatermarkNone_Checked">None</RadioButton>
                <RadioButton GroupName="waterMarkType" IsChecked="{Binding Path=watermarkType, Converter={StaticResource EnumConverter}, ConverterParameter=Text}" Name="rbtwatermarkText" Checked="rbtwatermarkText_Checked" >Text</RadioButton>
                <RadioButton GroupName="waterMarkType" IsChecked="{Binding Path=watermarkType, Converter={StaticResource EnumConverter}, ConverterParameter=Image}" Name="rbtwatermarkImg" Checked="rbtwatermarkImg_Checked" >Photo</RadioButton>
            </StackPanel>