Also, even for your embedded 1st-party images, even if you really know every variation you want to deliver (putting you in a small minority), and you already have an asset pipeline you're happy with (a smaller minority), there are still potential use cases (test automation, R&D, prototyping, DX shortcuts...) I can think of off the top of my head.

No affiliation (I haven't even tried Pixaven), just replying to your question per se. :)

Edit: also, some of the listed features (eg face detection and blurring) might not be part of your extant pipeline's capabilities.

Pixaven is a service meant (ideally) for businesses running at scale. If you're a large e-commerce platform with literally millions of new images (and their variants) created per day you would be looking for a solid platform to process this visual content for you.