Image colocation support in eleventy. See https://micheleong.com/2023/09/23/migrate-wordpress-eleventy-colocated-images

eleventy.config.js

// Import this
const modifyToken = require('markdown-it-modify-token');

module.exports = function (config) {
  ...
  // Pass a custom instance of markdownIt into eleventy.
  config.setLibrary("md", markdownIt({
    // html, breaks, and linkify are default options from eleventy.
    html: true,
    breaks: true,
    linkify: true,
    // This will prepend the colocated image path with the built asset path
    modifyToken: function (token, env) {
      switch (token.type) {
        case 'image':
          // Only apply this transform to relative image path
          // Regex explained: https://regex101.com/r/EM83AR/1
          if (token.attrObj.src.match(/^(?!www\.|(?:http|ftp)s?:\/\/|[A-Za-z]:\\|\/).*/)) {
            // https://www.11ty.dev/docs/data-eleventy-supplied/#filepathstem
            const stem = env.page.filePathStem.split(path.sep);
            stem.pop();
            token.attrObj.src = path.resolve(stem.join(path.sep), token.attrObj.src);
          }
          break;
        }
      }
    })
    .use(modifyToken)
  );

  // This copies your images from where they are colocated to a similarly pathed location in `dist`
	// It allows the modifyToken above and colocatedImagePath filter below to work.
	config.addPassthroughCopy('src/posts/**/images/*');
  
	// This adds a filter that performs a similar transform as modifyToken that you can use in templates
	config.addFilter('colocatedImagePath', (src, filePathStem) => {
		const stem = filePathStem.split(path.sep);
		stem.pop();
		return src ? path.resolve(stem.join(path.sep), src) : '/assets/img/no-image.svg';
	});
	...
};