A fingerprint class for versioning of static web content (derives from Mads Kristensen's Fingerprint class found here http://madskristensen.net/post/cache-busting-in-aspnet)

Fingerprint.cs

using System.IO;
using System.Web;
using System.Web.Caching;
using System.Web.Hosting;

public static class Fingerprint
{

	public static string Tag(string rootRelativePath)
	{
		if (null == HttpRuntime.Cache[rootRelativePath])
		{
			var absolute = HostingEnvironment.MapPath("~" + rootRelativePath);
			var dateLastWrite = File.GetLastWriteTime(absolute);
			var result = VirtualPathUtility.ToAbsolute(
				string.Format("~{0}?{1}", 
					rootRelativePath, 
					dateLastWrite.Ticks));
			HttpRuntime.Cache.Insert(
				rootRelativePath, 
				result, 
				new CacheDependency(absolute));
		}
		return HttpRuntime.Cache[rootRelativePath] as string;
	}

}