Private Sub LoadImage()

    If Application.Current.HasElevatedPermissions Then
        Dim di As New DirectoryInfo(Environment.GetFolderPath(Environment.SpecialFolder.MyPictures))

        Dim files = From f In di.EnumerateFiles() _
            Where f.Extension.ToLower() = ".jpg" OrElse f.Extension = ".png" _
            Select f

        Dim max As Integer = files.Count() + 1

        Dim rnd As New Random()
        Dim r As Integer = rnd.[Next](0, max)

        Dim pics As New List(Of FileInfo)(files)

        Dim randpic As String = pics(r).FullName

        Dim img As New BitmapImage()
        img.SetSource(New FileStream(randpic, FileMode.Open))


        MyImage.Source = img
    End If
End Sub

private void LoadImage()
{

    if (Application.Current.HasElevatedPermissions)
    {
        DirectoryInfo di = new DirectoryInfo(Environment.GetFolderPath(
           Environment.SpecialFolder.MyPictures));

        var files = from f in di.EnumerateFiles()
                    where f.Extension.ToLower() == ".jpg" || 
                        f.Extension == ".png"
                    select f;

        int max = files.Count() + 1;

        Random rnd = new Random();
        int r = rnd.Next(0, max);

        List<FileInfo> pics = new List<FileInfo>(files);

        string randpic = pics[r].FullName;

        BitmapImage img = new BitmapImage();
        img.SetSource(new FileStream(randpic, FileMode.Open));

        MyImage.Source = img;

    }
}