Problem with Image not refreshing

Private Function GenerateVCodeImage() As String
 
	Dim bmfile As String = Server.MapPath("~") & "\capimage.jpg"
	Dim txfile As String = Server.MapPath("~") & "\captext.txt"
	Dim oBitmap As Drawing.Bitmap = New Drawing.Bitmap(90, 35)
	Dim oGraphic As Drawing.Graphics = Drawing.Graphics.FromImage(oBitmap)
	Dim foreColor As System.Drawing.Color
	Dim backColor As System.Drawing.Color
 
	Dim sText As String = generateVCode(5)
	Dim sFont As String = "Comic Sans MS"
 
	foreColor = System.Drawing.Color.FromArgb(220, 220, 220)
	backColor = System.Drawing.Color.FromArgb(190, 190, 190)
 
	Dim oBrush As New Drawing.Drawing2D.HatchBrush(CType(generateHatchStyle(), Drawing.Drawing2D.HatchStyle), foreColor, backColor)
	Dim oBrushWrite As New Drawing.SolidBrush(Drawing.Color.Red)
 
	oGraphic.FillRectangle(oBrush, 0, 0, 100, 50)
	oGraphic.TextRenderingHint = Drawing.Text.TextRenderingHint.AntiAlias
 
	Dim oFont As New Drawing.Font(sFont, 14)
	Dim oPoint As New Drawing.PointF(5.0F, 4.0F)
 
	oGraphic.DrawString(sText, oFont, oBrushWrite, oPoint)
 
	Response.ContentType = "image/jpeg"
	oBitmap.Save(bmfile, Drawing.Imaging.ImageFormat.Jpeg)
	oBitmap.Dispose()
 
	verimg.ImageUrl = "capimage.jpg"
	File.WriteAllText(txfile, sText)
	Return sText
 
End Function
 
 
Private Function generateVCode(ByVal CodeLength As Integer) As String
	Dim VCode As String = String.Empty
	Dim randObj As New Random()
	Dim c As Integer = 63
	For i As Byte = 1 To CodeLength
		c = randObj.Next(35)
		If c >= 10 Then
			c += 7
		End If
		c += 48
		VCode += Chr(c)
	Next
	Return VCode
End Function
 
Private Function generateHatchStyle() As HatchStyle
	Dim slist As New ArrayList
	For Each style As HatchStyle In System.Enum.GetValues(GetType(HatchStyle))
		slist.Add(style)
	Next
 
	Dim randObj As New Random()
	Dim index As Integer = randObj.Next(slist.Count - 1)
 
	Return CType(slist(index), HatchStyle)
End Function