Public Class Form1
    Dim images() As String = New String() {}
    Dim currentImageIndex As Integer = 0

    Private Sub ZakończToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles ZakończToolStripMenuItem.Click
        If MessageBox.Show("Czy jesteś pewien?", "Komunikat", MessageBoxButtons.YesNo, MessageBoxIcon.Question) = DialogResult.Yes Then
            Application.Exit()
        End If
    End Sub

    Private Sub PrzegladarkaGrafikiInfoToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles PrzegladarkaGrafikiInfoToolStripMenuItem.Click
        MessageBox.Show("Program do przeglądania grafiki." & vbNewLine & "Autor: XYZ")
    End Sub

    Private Sub OtwórzToolStripMenuItem_Click(sender As Object, e As EventArgs) Handles OtwórzToolStripMenuItem.Click
        OpenFileDialog1.FileName = ""
        OpenFileDialog1.Filter = "Pliki graficzne|*.jpg;*.bmp;*png|Wszystkie pliki|*.*"
        If OpenFileDialog1.ShowDialog() = DialogResult.Cancel Then
            Exit Sub
        End If

        SaveImage(OpenFileDialog1.FileName)
        ShowCurrentImage()
    End Sub

    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        If currentImageIndex > 0 Then
            currentImageIndex = currentImageIndex - 1
        End If

        ShowCurrentImage()
    End Sub

    Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
        If currentImageIndex < images.Length - 1 Then
            currentImageIndex = currentImageIndex + 1
        End If

        ShowCurrentImage()
    End Sub

    Private Sub SaveImage(fileName As String)
        ReDim Preserve images(0 To UBound(images) + 1)
        currentImageIndex = UBound(images)
        images(currentImageIndex) = fileName
    End Sub

    Private Sub ShowCurrentImage()
        PictureBox1.Image = Image.FromFile(images(currentImageIndex))
    End Sub
End Class