Server-side Image Manipulation?

Is it possible to perform simple image manipulation - e.g. crop and scale - using Wix code? A glance at the API reference suggested not, but I thought I’d check to be sure.

No, it´s not, and you are not the only one who wants it. It´s a necessary part of a development environment, since people will not hesitate to upload a 10 Mb foto when it is only displayed as a small profile pic, thereby making page load slower than nec., not to speak of used disk space.
The issue has been raised here before, we can only hope.

We don’t currently allow croping and scaling via code, BUT what @Giri wrote is not accurate. Wix is already doing most of the heavy lifting in this area for you - The image will be optimized to fit its view, Wix doesn’t simply download the image as is and uses it.
In the attached image you can see how I used the same image twice, and Wix made the optimization and returned a smaller image when needed: