Requested feature overview description.
An auto-resizing option would be great, and probably not too hard to make. Essentially, what I want is a "fit to screen" option, but the name "auto" would be better suiting. Behind the scenes it just needs to switch between the "Fit (Horizontal)" and "Fit (Vertical)" options depending on which dimension of the image is larger. It would need to be able to handle the edge case of a 1:1 image.

It might also be nice for it to have limits. For example, if the image is tall and thin, instead of vertical fit ike it would usually do, it could resize to a horizontal fit instead.

Essentially; whenever a horizontal or vertical fit makes the image go offscreen in a smaller amount (depends on the aspect ratio, but for example, a 16:10 image on a 16:9 display) it will fix the fit to make it all fit on screen. but if it there is an image that has very large aspect ratio, it will just do the opposite, and set it to the fit that needs less zooming.

Why would it be useful?
This could allow for viewing most images without needing to scroll.

What part(s) of the site page(s) are affected?
The post viewer would change

PS: If this has already been suggested or anything, I'm sorry. I search around for keywords on this and didn't find anything. If it is a duplicate, please make sure post a link to the original.