<Grid>
  <DockPanel>
   <Menu DockPanel.Dock="Top">
    <Menu>
     <MenuItem Header="_Open" Command="{Binding OpenFileCommand}"/>
    </Menu>
    <Menu>
     <MenuItem Header="_ZoomIn" Command="{Binding ZoomCommand}" CommandParameter="ZoomIn"/>
    </Menu>
    <Menu>
     <MenuItem Header="_ZoomOut" Command="{Binding ZoomCommand}" CommandParameter="ZoomOut"/>
    </Menu>
    <Menu>
     <MenuItem Header="_Normal" Command="{Binding ZoomCommand}" CommandParameter="Normal"/>
    </Menu>
   </Menu>
   <ScrollViewer>
    <Image Source="{Binding ImagePath}" Stretch="None">
     <Image.LayoutTransform>
      <ScaleTransform ScaleX="{Binding Zoom}" ScaleY="{Binding Zoom}"/>
     </Image.LayoutTransform>
    </Image>
   </ScrollViewer>
  </DockPanel>
 </Grid>

 public class ViewModelBase : INotifyPropertyChanged
 {
  public event PropertyChangedEventHandler PropertyChanged;
  protected virtual void OnPropertyChanged(string propName)
  {
   if(PropertyChanged!=null)
   {
    PropertyChanged(this, new PropertyChangedEventArgs(propName));
   }
  }
 }

public class OpenFileCommand : ICommand
 {
  private MainViewModel _data;
  public OpenFileCommand(MainViewModel data)
  {
   _data = data;
  }
  public event EventHandler CanExecuteChanged;
  public bool CanExecute(object parameter)
  {
   return true;
  }
  public void Execute(object parameter)
  {
   OpenFileDialog dialog = new OpenFileDialog() { Filter = "Image Files|*.jpg;*.png;*.bmp;*.gif" };
   if(dialog.ShowDialog().GetValueOrDefault())
   {
    _data.ImagePath = dialog.FileName;
   }
  }

 public enum ZoomType
 {
  ZoomIn = 0,
  ZoomOut = 1,
  Normal = 2
 }
 public class ZoomCommand : ICommand
 {
  private MainViewModel _data;
  public ZoomCommand(MainViewModel data)
  {
   _data = data;
  }
  public event EventHandler CanExecuteChanged
  {
   add { CommandManager.RequerySuggested += value; }
   remove { CommandManager.RequerySuggested -= value; }
  }
  public bool CanExecute(object parameter)
  {
   return _data.ImagePath != null;
  }
  public void Execute(object parameter)
  {
   ZoomType type = (ZoomType)Enum.Parse(typeof(ZoomType), (string)parameter, true);
   switch(type)
   {
    case ZoomType.Normal:
     _data.Zoom = 1;
     break;
    case ZoomType.ZoomIn:
     _data.Zoom *= 1.2;
     break;
    case ZoomType.ZoomOut:
     _data.Zoom /= 1.2;
     break;
   }
  }
 }

public class MainViewModel : ViewModelBase
 {
  private string _imagePath;
  public string ImagePath
  {
   get
   {
    return _imagePath;
   }
   set
   {
    if (_imagePath != value)
    {
     _imagePath = value;
     OnPropertyChanged("ImagePath");
    }
   }
  }
  private double _zoom = 1.0;
  public double Zoom
  {
   get
   {
    return _zoom;
   }
   set
   {
    if(_zoom != value)
    {
     _zoom = value;
     OnPropertyChanged("Zoom");
    }
   }
  }
  private ICommand _openFileCommand;
  public ICommand OpenFileCommand
  {
   get { return _openFileCommand; }
  }
  private ZoomCommand _zoomCommand;
  public ZoomCommand ZoomCommand
  {
   get { return _zoomCommand; }
  }
  public MainViewModel()
  {
   _openFileCommand = new OpenFileCommand(this);
   _zoomCommand = new ZoomCommand(this);
  }
 }

 public MainWindow()
  {
   InitializeComponent();
   DataContext = new MainViewModel();
  }

  public App()
  {
   MainWindow window = new MainWindow();
   window.DataContext = new MainViewModel();
   window.Show();
  }