You should assign the image in the code behind file like:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

If Request.QueryString("YourParameterName") IsNot Nothing Then
Image1.ImageUrl = Request.QueryString("YourParameterName")
Image1.Visible = True
Else
Image1.Visible = False
End If

End Sub