code: function(imageIdentifier, callback) {
          this.headImage(imageIdentifier, function(err, res) {
              if (err) {
                  return callback(err);
              }
  
              var headers = res.headers,
                  prefix = 'x-imbo-original';
  
              callback(err, {
                  width: parseInt(headers[prefix + 'width'], 10),
                  height: parseInt(headers[prefix + 'height'], 10),
                  filesize: parseInt(headers[prefix + 'filesize'], 10),
                  extension: headers[prefix + 'extension'],
                  mimetype: headers[prefix + 'mimetype']
              });
          });
  
          return this;
      }
docs: Get properties about an image stored in Imbo
  
  @param {String}   imageIdentifier
  @param {Function} callback
  @return {ImboClient}