A number of folks have reported that the photos at the top of each post were appearing upside-down to them. I believe I have now fixed this for all new posts; if you see this issue for anything posted from Day 26 and later, please let me know by commenting on this post. Also, thank you to the people who let me know about it! I only have my iPhone with me, and they (of course) always display correctly for me.
Also, for anyone not clicking through to the full posts, note that I post galleries of anywhere between a few and several dozen photos at the end of each day, both on Flickr and embedded at the bottom of each post.
Technical folks: Obviously the problem was with EXIF rotation data either not getting applied or getting double-applied somewhere, but I’m not sure where. The fix I found was to upload photos via the WordPress iOS app, rather than via the WordPress mobile admin Web interface, which was causing the issues. My workflow was: Mobile Safari -> WP Admin, then published to WordPress, running the Blogoma theme which (I believe) provides the gallery control (almost certainly some third-party JS library), then served up via WP, nginx, and CloudFlare. There are too many links in this chain for me to really know exactly where the problem is or was, but I seem to have found a workaround, and that’s really all that matters.