UpdatePanel working only on Chrome and not in IE / Mozilla. Why? - asp.net

Question

On Clicking the LinkButton, I refresh the image in image control without refreshing the page. For this I have used the UpdatePanel and AsyncPostBackTrigger.
It is working perfectly in chrome. But not in IE and Mozilla. On both IE and Mozilla when I click the link button, nothing happens. Look very weird. Have any clue on this ?
<asp:UpdatePanel ID="UpdatePanel1" runat="server" UpdateMode="Conditional">
<ContentTemplate>
<asp:TextBox ID="txtCaptchaInput" BorderStyle="Solid" Style="vertical-align: top" runat="server" Width="106px" BorderWidth="1px"></asp:TextBox>
<asp:Image ID="img_captcha" runat="server" Height="32px" ImageUrl="~/captchaJPEG.aspx" Width="108px" />
<asp:LinkButton ID="captcha_refresh" runat="server">Refresh Image</asp:LinkButton>
</ContentTemplate>
<Triggers>
<asp:AsyncPostBackTrigger ControlID="captcha_refresh" />
</Triggers>
</asp:UpdatePanel>
CaptchaJPEG.aspx : Page Load
Dim captcha As New Captcha.CaptchaImage()
captcha.width = 150
captcha.height = 40
captcha.text = Me.Session("CaptchaText").ToString()
captcha.GenerateImage()
captcha.image.Save(Me.Response.OutputStream, System.Drawing.Imaging.ImageFormat.Jpeg)

Answer 1

Your issue have to do with the caching of the captchaJPEG.aspx that return an image. As image the browser can keep it and not change it.
To avoid that you have two ways, you can set some cache headers to say to the browser to not keep it on the cache as:
Response.Cache.SetExpires(DateTime.Now.AddDays(-10));
Response.Cache.SetMaxAge(new TimeSpan(-10, 0, 0));
Or -that I think is better- add a random number on the image tag as you set it on code behind, as:
img_captcha.ImageUrl = "~/captchaJPEG.aspx?_rnd=" + RandomNumber;
Here you can make something even better, to use the hash() of your code captcha, as:
img_captcha.ImageUrl = "~/captchaJPEG.aspx?_rnd=" + CaptachHiddenNumbers.hash();
Thats way you keep it on cache if the captcha is the same from load to load.
Now, the "correct way" is to use a handler and not a page for many reasons, like you do not want all the overhead of the page just to send an image. Now the handler come with the minimum modules call, to add session you need to use the IRequiresSessionState.
To answer to the question, why is acting different on the browsers, is because in some small details browser have different behavior, is depend how and what they check to make a decision to use the cached images and how aggressive are the browser with the cache.