What image sizes do you generate and how do you serve them?

Question

Yii

For desktops, tablets, smartphones, previews. And how after that to give the necessary?
What are the best options?

Answer 1

fullsize is stored on the disk, clients ask for the dimension, if there is already one, it gives it to nginx, if not, it creates the back and puts it in the cache.

Answer 2

On the fly + caching