In checking the source code of my own Ghost blog, I found the images were already responsive-- a srcset tag was there specificying different image sizes based on CSS media queries.
Forcing images into the webp option does not appear to be configurable now, and how you might alter the code to do it would depend on whether you work with the old/current editor the new Lexical editor.
Some related things to look for in the code are were Lexical processes images:
You can also see there a references to the internal image-transform library, which is involved.
You might also look into Ghost’s support for storage adapters. I’m not sure if storage adapters are allowed to change the image format or not.
Does it mean there is no way to do it right now?
Article page becomes very heavy on images and hits low PageSpeed scores. Those pages are the main driver of organic traffic. Did anyone try to optimise them somehow?
If you’re looking for speed try Bunny Optimizer for $10/month, basically set your regular site URL as Origin and edit the Ghost-theme to fetch images over Bunny’s CDN - images will be pulled from your site, converted and delivered as WebP-format, so…
Delivers a PNG
Delivers a WEBP
Filetype / extension will not change, the MIME-type will. And the file size ;)
I’m using Bunny CDN and get PageSpeed 98, wrote a post about it…