C# と VB.NET の質問掲示板

タイトルが最大入力可能数を超えたので改めて書きますが、
ピクチャボックス(PicWaku)内にグラフィックで書いた線などの下側にJPEGなどの画像ファイルを呼び出したいのですが、画像ファイルがグラフィックで書いた線の上になって線が消えてしまいます。

Public Class Form1
    Inherits System.Windows.Forms.Form
    Dim gra As Graphics
    Dim drawFlg As Boolean
    Dim x1 As Integer = -1, y1 As Integer
    Dim x2 As Integer = -1, y2 As Integer
    Dim mypen As New Pen(Color.Black, 2)
(中略)
　　'起動
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles MyBase.Load
        With picWaku
            .Image = Nothing
            .SizeMode = System.Windows.Forms.PictureBoxSizeMode.AutoSize
            .Image = New Bitmap(picWaku.Width, picWaku.Height)
            gra = Graphics.FromImage(.Image)
            gra.Clear(Color.White)
        End With
    End Sub

    Private Sub PicWaku_MouseMove(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PicWaku.MouseMove
        If drawFlg = True Then
            gra.DrawLine(mypen, x2, y2, e.X, e.Y)
            x2 = e.X : y2 = e.Y
            picWaku.Refresh()
        End If
    End Sub
    Private Sub PicWaku_MouseUp(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PicWaku.MouseUp
        drawFlg = False
        picWaku.Refresh()
    End Sub
   Private Sub PicWaku_MouseDown(ByVal sender As System.Object, ByVal e As System.Windows.Forms.MouseEventArgs) Handles PicWaku.MouseDown
            x2 = e.X : y2 = e.Y
            drawFlg = True
End Sub

　　'画像を呼び出すボタン(cmdRoad)
　　'このボタンを押したとき、マウスで書いた図形の下に画像を呼び込む
    Private Sub cmdRoad_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdRoad.Click
        Dim MyPath As String = Application.StartupPath
        Dim inifilepath As String
        If MyPath.EndsWith("\") = False Then
            MyPath &= "\"
        End If
        inifilepath = MyPath & "seikai.jpg"
        If System.IO.File.Exists(inifilepath) = True Then
            PicWaku.Image = Image.FromFile(inifilepath)
            'PicWaku.Image = PicWaku.Image
        End If
    End Sub

　　'終了するボタン(cmdExit)
    Private Sub cmdExit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles cmdExit.Click
        Application.Exit()
    End Sub


    Dim gra As Graphics
の gra を上手く使えば出来そうですが。

アドバイスをお願いします。