All credit goes to @kentcdodds ! I just extracted the code from this [commit](https://github.com/kentcdodds/kentcdodds.com/commit/d7ebfcc7e3e8fb8354f0ca58da8159fccaeeb14d#) for personal use :D

boom-images.js

import path from 'path'
import cloudinary from 'cloudinary'
import glob from 'glob'
import fs from 'fs'
import os from 'os'

const directoryCache = {}
const existingFolders = new Set()

cloudinary.config({
  cloud_name: 'xxxxxx',
  api_key: 'xxxxxx',
  api_secret: 'xxxxxx',
  secure: true,
})

const repoDirParentDir = path.join(os.homedir(), 'code')

const mdxFilePaths = glob.sync(
  path.join(repoDirParentDir, 'kentcdodds.com/content/**/*.mdx'),
)

for (const mdxFilePath of mdxFilePaths) {
  console.log('starting work on', mdxFilePath)
  const content = await fs.promises.readFile(mdxFilePath, 'utf8')
  const banner = content.match(/banner: '?(\.\/.*?)'?$/m)?.[1]
  const metaImage = content.match(/metaImage: '?(\.\/.*?)'?$/m)?.[1]
  const guestPhoto = content.match(/guestPhoto: '?(\.\/.*?)'?$/m)?.[1]
  const inPostImages = (content.match(/!\[.*?\]\(\.\/(.*?)\)/g) ?? []).map(
    s => s.match(/\((.*)\)/)[1],
  )
  const images = [banner, metaImage, guestPhoto, ...inPostImages]
    .filter(Boolean)
    .map(image => ({
      relativePath: image,
      fullPath: path.join(path.dirname(mdxFilePath), image),
    }))
  if (!images.length) continue

  const cloudinaryFolder = mdxFilePath
    .replace(`${repoDirParentDir}/`, '')
    .replace('/index.mdx', '')

  const foldersToCreate = new Set()
  for (const image of images) {
    const cloudinaryParentPath = getCloudinaryParentPath(
      cloudinaryFolder,
      image.relativePath,
    )
    foldersToCreate.add(cloudinaryParentPath)
  }
  await Promise.all(
    Array.from(foldersToCreate).map(async folderToCreate => {
      if (!existingFolders.has(folderToCreate))
        await createFolder(folderToCreate)
    }),
  )

  const uploadedImages = await Promise.all(
    images.map(async image => {
      const cloudinaryParentPath = getCloudinaryParentPath(
        cloudinaryFolder,
        image.relativePath,
      )
      const uploadedImage = await uploadFile(
        image.fullPath,
        cloudinaryParentPath,
      )
      return {
        ...image,
        url: uploadedImage.secure_url,
      }
    }),
  )
  let newContent = content
  for (const image of uploadedImages) {
    newContent = newContent.replace(image.relativePath, image.url)
  }
  newContent = newContent.replace(/banner: /, 'bannerUrl: ')
  await fs.promises.writeFile(mdxFilePath, newContent)
  const percent = (
    ((mdxFilePaths.indexOf(mdxFilePath) + 1) / mdxFilePaths.length) *
    100
  ).toFixed(2)
  console.log(`${percent}% complete`)
}

function getCloudinaryParentPath(cloudinaryFolder, relativePath) {
  const cloudinaryImagePath = path.join(cloudinaryFolder, relativePath)
  // most images are in a /images directory and that extra nesting
  // doesn't make sense on cloudinary
  return path.parse(cloudinaryImagePath).dir.replace('/images', '')
}

async function createFolder(fullPath) {
  const result = await cloudinary.v2.api.create_folder(fullPath)
  existingFolders.add(fullPath)
  return result
}

async function uploadFile(filePath, folder) {
  const uploadedImage = await cloudinary.v2.uploader.upload(filePath, {
    public_id: path.parse(filePath).name,
    overwrite: true,
    folder,
  })
  return uploadedImage
}

process.on('unhandledRejection', error => {
  console.error(error.stack)
})