For me, lack of nice (ie. controllable, but 'automagic') image handling is a huge bug bear in nearly every cms out there, static or otherwise. Perhaps I didn't find the right platform/plugin...
In my case, I wanted to have 1 source image that was resized at various (author controllable) sizes and then saved them, while also generating supporting HTML (eg. 'srcset' to automatically swap between them). I ended up with a couple of ways to template it in [0]:
For a thumbnail:
<img src="{{image #thumb{w:50} }}">
For srcset:
<img src="{{image}}" srcset="{{image #srcset{w:'256,512,800',orig:'1152'} }}" sizes=...>
[0] https://github.com/ergo-cms/plugin-thumbnail. (Note the entire project itself stalled some time ago, and wouldn't recommend it here -- even though I do dogfood it)
EDIT: reorder wording