Prova così:
codice:
Private moving As Boolean
Private old_x As Single, old_y As Single

Private Sub Image1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
   moving = True
   old_x = X
   old_y = Y
End Sub

Private Sub Image1_MouseMove(Button As Integer, Shift As Integer, X As Single, Y As Single)
   If (Button = 1) And moving Then
      Image1.Left = Image1.Left - (old_x - X)
      Image1.Top = Image1.Top - (old_y - Y)
   End If
End Sub

Private Sub Image1_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
   moving = False
End Sub