Some discussion in https://gerrit.wikimedia.org/r/c/mediawiki/services/parsoid/+/593576/5/tests/phpunit/Parsoid/Config/SiteConfigTest.php#315
All of the img_* options (right, left, etc) are case-sensitive (only lower-case allowed) *except* for img_lossy, which is case-insensitive (lossy, LOSSY, lOsSy etc allowed).
We should make img_lossy case-sensitive for consistency. (Or we could make all the options case-insensitive, but I don't see a strong reason to do that.)