I've gotten asked "how can we manage variations of images with Tridion" in my most recent trainings.
And the answer is typically with 2 options: - multiple images (small/large, thumbnail/full, etc) - image variants -- at publish you can render different sizes
Tridion delivery-side features for managing variations of images along with caching
a use case could be to complement a Responsive Web Design approach with smaller or optimized images for the visitor's context (device/browser/whatever)