For use on blog post: http://normansolutions.co.uk/post/cache-busting-in-c-without-querystrings

FingerPrint.cs

public static string FingerPrint(string rootRelativePath, string cdnPath = "")
{
    if (!string.IsNullOrEmpty(cdnPath) && !HttpContext.Current.IsDebuggingEnabled)
    {
        return cdnPath;
    }
        if (HttpRuntime.Cache[rootRelativePath] == null)
    {
        string relative = VirtualPathUtility.ToAbsolute("~" + rootRelativePath);
        string absolute = HostingEnvironment.MapPath(relative);
        if (!File.Exists(absolute))
        {
            throw new FileNotFoundException("File not found", absolute);
        }
        DateTime date = File.GetLastWriteTime(absolute);
        int index = relative.LastIndexOf('/');
        string result = relative.Insert(index, "/v-" + date.Ticks);
        HttpRuntime.Cache.Insert(rootRelativePath, result, new CacheDependency(absolute));
    }
        return HttpRuntime.Cache[rootRelativePath] as string;
}