We’re not advocating using ever changing URLs. What we’re saying is that you only change the URL if your resource/image has changed. In lots of cases images are almost never modified and they should be cached for as long as possible (e.g. Google caches their logo until 2038!). Changing the URL provides a way of forcing a client to update the resource if required.

It sounds like you have a special case where your images are subject to periodic change and it does not matter if your clients have the latest version.

I have a server that dishes out vehicle images from a large database of several million records. By caching image requests on both the server and the client (for a limited time only) performance is greatly enhanced. The last thing I want is hundreds of clients simultaneously bombarding the server with ever-changing URLs just to make sure they have an up-to-date image. Instead they use the same URL each time for a given vehicle… On the majority of occasions that URL never even makes it out to the internet (because the content is cached on the client) and if hundreds of clients simultaneously request the same image from the server, the server only needs to do its work on the database once (because the content is cached on the server). At the same time, the limited cache duration ensures that the latest image is made available within an acceptable latency period if it does change.

By the way, HttpWatch has been invaluable in making sure that this all works as planned!