<img src='PTCL-3.jpg?websiteversion=<%=DateTime.Now.Ticks.ToString()%>' alt="Sample Image" />
This will solve your problem and you will always get updated images. But the problem with this approach is that your images, CSS and java script will be downloaded for every request which will slowdown your site's performance.
Now, here is how you can solve both the problems, Add a key in appSettings section of your wen.config file like this:-
<appSettings> <add key="WebsiteVersion" value="1"/> </appSettings>
And add the parameter to your images, CSS and java script files like this:-
<img src='PTCL-3.jpg?websiteversion=<%=System.Configuration.ConfigurationSettings.AppSettings["WebsiteVersion"] %>' alt="Sample Image" />
Now whenever you change any Image, CSS or .js file you have to update the WebsiteVerion value in your web.config file.
Do share your comments, happy coding !!!