Web Forms :: Loading HTML Files Dynamically From Codebehind?

i would like to load a banner on to the page based on the registration count we have in the DB. if the registration count is >70, i will have to load banner2 on to the page. i am doing like this On the webForm.aspx

<img src="images/banner1.jpg"
runat="server"
id="imgs"/>

in the code behind

protected void Page_Load(object sender,
EventArgs e){
if (!Page.IsPostBack)
{
if(isSessionOneFilled())
{
imgs.Src = "images/banner2.jpg";
}
}
}

The above code works. is it Good Programming to load html files from codebehind? is there any alternative way? how does this impact when internet speed is slow?