code: function (callback) {
          if (!self._image) {
            var paths = (process.env.PATH || '').split(delimiter);
            if (!_.find(paths, function(p) {
              if (fs.existsSync(p + '/imagecrunch')) {
                self._image = require('./lib/image/imagecrunch.js')();
                return true;
              }
              // Allow for Windows and Unix filenames for identify. Silly oversight
              // after getting delimiter right (:
              if (fs.existsSync(p + '/identify') || fs.existsSync(p + '/identify.exe')) {
                self._image = require('./lib/image/imagemagick.js')();
                return true;
              }
            })) {
              // Fall back to jimp, no need for an error
              self._image = require('./lib/image/jimp.js')();
            }
          }
          return callback(null);
        }
docs: Autodetect image backend if necessary