Private Declare Function ReleaseCapture Lib "user32" () As Long
Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
  (ByVal hwnd As Long, ByVal wMsg As Long, ByVal wParam As Long, _
  lParam As Any) As Long

Private Const WM_NCLBUTTONDOWN = &HA1
Private Const HTBOTTOMRIGHT =  17 

Private Sub Pic_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
    '  Снимает текущий захват мыши
    ReleaseCapture
    '  Посылает сообщение, окну (Me.hwnd) какбудто левая кнопка мыши (WM_NCLBUTTONDOWN)
    '  опущена на нижний правый (HTBOTTOMRIGHT) угол окна
    SendMessage Me.hwnd, WM_NCLBUTTONDOWN, HTBOTTOMRIGHT,  0 
End Sub