I'm looking for a way to create an image resize service based on DO Object Storage.

Is it possible to froward all image requests to the storage and when the file is not found redirect request to the resizing backend?

It's similar to the Nginx config:

 # check if image already exists 
 location ~ /(\d+x\d+/.*) {
    try_files /$1 @img;
  }

  # This saves the resized image locally.
  location @img {    
    proxy_pass $full_uri;
    proxy_store /var/www/cache/store/img/$full_uri;
  }