[jiggawatts]

You can have a separate system, even a locally running desktop app do that. You can still have a database, complex HTML templating, and image resizing! You just do it offline as a preprocessing step instead of online dynamically for each page view.

Unfortunately, this approach never took off, even though it scales trivially to enormous sites and traffic levels.

I recently tried to optimise a CMS system where it was streaming photos from the database to the web tier, which then resized it and even optimised it on the fly. Even with caching, the overheads were just obscene. Over a 100 cores could barely push out 200 Mbps of content. Meanwhile a single-core VM can easily do 1 Gbps of static content!