Al fin lo conseguí, es tan simple como esto.
Dim x1 As Single, y1 As Single
Private Sub Form_DragDrop(Source As Control, X As Single, Y As Single)
Source.Move X - x1, Y - y1
Source.Visible = True
End Sub
Private Sub Picture1_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single)
If Button = vbLeftButton Then
x1 = X
y1 = Y
Picture1.Drag vbBeginDrag
Picture1.Visible = False
Picture1.Drag
End If
End Sub