cid-example.js

var params = {
  smtpapi:  new sengrid.SmtpapiHeaders(),
  ... //some vars removed here!
  files: [
    {
      filename:     'image.jpg',          
      contentType:  'image/jpeg',
      cid:          'myimagecid',
      content:      ('yourbase64encodedimageasastringcangohere' | Buffer)
    }
  ],
  file_data:  {},
  headers:    {}
};