To configure, go to your Vercel dashboard, project settings, and add env vars IMAGEFLOW_AWS_ACCESS_KEY_ID and IMAGEFLOW_AWS_ACCESS_KEY_SECRET with your AWS access key ID and secret respectively.
To use, visit
/api/imageflow/[region]/[bucket]/[path/to/image.jpg]?width=200
Uses the same querystring commands as ImageResizer 4, plus a few more.