I am delighted that you chimed in here; these are pleasingly composed and increase my desire to read the relevant sequences. Your post makes me feel like I meaningfully contributed to the improvement of these sequences by merely asking a potentially dumb question in public, which is the internet at its very best.
Artistically, I think the top (fox face) image for lotteries cropped for its bottom 2⁄3 would be slightly preferable to the other, and the bottom (monochrome white/blue) for geometric makes a nicer banner in the aspect ratio that they’re shown as.
I notice that I am confused: an image of lily pads appears on https://www.lesswrong.com/s/XJBaPPEYAPeDzuAsy when I load it, but when I expand all community sequences on https://www.lesswrong.com/library (a show-all button might be nice....) and search the string “physical” or “necessity” on that page, I do not see the post appearing. This seems odd, because I’d expect that having a non-default image display when the sequence’s homepage is loaded and having a good enough image to appear in the list should be the same condition, but it seems they aren’t identical for that one.