oops
apparently when I (finally) added smaller versions of of photos for my website, I did it in a way that broke portrait photos. Weirdly they look right in my feed reader but not on my site.
I think I know what's happening. My camera stores all photos in landscape resolution and sets a flag for rotation in the EXIF data. My naive file conversion isn't doing anything about this and thus the resulting webp file is also in landscape. That EXIF rotation data isn't used by default (or is even out of spec?) for webp so at least in firefox on a mac it renders as horizontal on my website. My feed reader is actually using that EXIF data and fixing it? That's my guess without actually testing anything anyway.
I'll fix it by the next time I upload photos since that probably broke a tone of older pages