Get Javascript changes to ASP.Net control on postback

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ASP.NET

web_development

I am writing a page where users can update their profile for a simple chat board. There is an asp:Image control which is loaded with the user's current avatar. On the same page is a list of available avatar images; each is a standard HTML img tag with the following attribute:

onclick='setAvatar(this);'

The function itself looks like this:

function setAvatar(e) {
    var file = e.getAttribute('src');
    var img = document.getElementById('ctl00_ContentHolder_UserAvatar');
    img.src = file;
    return true;
}

In this script, file is the src attribute for the stock image being clicked, and img is the asp:Image control that displays the current or newly selected avatar image. This all works fine and dandy: clicking on a stock image changes the image displayed on the control.

My problem occurs when the user clicks the Save button and a postback occurs. Because the change is made in the browser, it is not reflected in the ViewState and so gets lost.

What I want is to let the user select an image and then update his profile with only the single postback that happens when clicking Save. Is there any way I can get there?