Dim S As String

    Function split_before(ByVal before)
        Dim mystr As String = TextBox1.Text
        Dim cut_at As String = """" & " frameborder"
        Dim x As Integer = InStr(mystr, cut_at)

        Dim string_before As String = mystr.Substring(0, x - 2)
        Return string_before
    End Function

    Function split_after(ByVal after)
        Dim mystr As String = S
        Dim cut_at As String = "src=" & """"
        Dim x As Integer = InStr(mystr, cut_at)

        Dim string_after As String = mystr.Substring(x + cut_at.Length - 1)
        Return string_after
    End Function

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Try
            S = split_before("""" & " frameborder")
            TextBox1.Clear()
            TextBox1.Text = split_after("src=" & """")
            Clipboard.SetText(split_after("src=" & """"))
        Catch ex As Exception

        End Try
    End Sub