(nodeJS) Content-Type for S3 object: manually set to ‘image/jpeg’ but in S3 console comes up as ‘application/octet’

Don’t set it in the Metadata section, that’s only for properties that will be prefixed with x-amz-meta. There is a ContentType parameter at the main level, like so:

var s3 = new AWS.S3();
var params = {
  Body: buffer,
  Bucket: <bucket>,
  Key: <key>,
  ContentType: 'image/jpeg'
};
s3.putObject(params, function(err, data) {
  if (err) console.log(err, err.stack); // an error occurred
  else  {
    console.log(data);
  }
})