code: function(checksum, callback) {
          var query = (new ImboQuery()).originalChecksums([checksum]).limit(1);
          this.getImages(query, function(err, images, search) {
              if (err) {
                  return callback(err);
              }
  
              var exists = search.hits > 0;
              callback(err, exists, exists ? images[0].imageIdentifier : err);
          });
  
          return this;
      }
docs: Checks if an image with the given MD5-sum exists on the server
  
  @param {String}   checksum
  @param {Function} callback
  @return {ImboClient}