Try this, Picture2 is the other PictureBox.
Code:
Private Sub Pic_MouseUp(Button As Integer, Shift As Integer, X As Single, Y As Single)
    With Picture2
        .Cls
        .PaintPicture Pic.Picture, 0, 0, EndX - StartX, EndY - StartY, _
                      StartX, StartY, EndX - StartX, EndY - StartY
    End With
End Sub