If you look at the images plugin fetched via npm, it's missing files in the build/workers directory.
❯ ls @elderjs/plugin-images/build
index.js index.mjs
But if you look at the markdown plugin, its utils directory is there.
❯ ls @elderjs/plugin-markdown/build
index.cjs index.d.ts index.js utils
Of note: the images plugin is not "type": "module". If you convert it to that, you'll have to fix the use of __dirname to use ESM-friendly stuff. Not sure if just doing that is enough to fix the build issue, or if something else is going on.