静态资源（图像）Web服务器的架构思想？

We're looking at removing all of the static resources (mainly images) in our ASP.NET 2.0 web app, and moving them to their own separate server. The main design requirements are for speed (so caching will be important) and a minimal level of security (so that people can't just directly download or rip off the images). Using a plain .net 2.0 web service immediately sprints to mind, but I'm worried about possible performance issues, and caching? Is this a valid concern?We're looking at removing all of the static res