Public Class Form1
 
    Private Sub Form1_Load(sender As Object, e As EventArgs) Handles MyBase.Load
        Button1.Enabled = False
        WebBrowser1.Navigate("https://s25.postimg.org/6v03o721b/OKIK_space.jpg")
    End Sub
 
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
 
        WebBrowser1.ShowSaveAsDialog()
    End Sub
 
    Private Sub WebBrowser1_Navigated(sender As Object, e As WebBrowserNavigatedEventArgs) Handles WebBrowser1.Navigated
        Button1.Enabled = True
    End Sub
End Class
 

Public Class Form1
    Dim WB As New WebBrowser
    Sub New()
        InitializeComponent()
        WB.Navigate("https://s25.postimg.org/6v03o721b/OKIK_space.jpg")
        AddHandler WB.DocumentCompleted, AddressOf WB_DocumentCompleted
    End Sub
 
    Private Sub WB_DocumentCompleted(sender As Object, e As WebBrowserDocumentCompletedEventArgs)
        WB.ShowSaveAsDialog()
    End Sub
End Class