Saving images locally in a Node.js executable

I'm writing a command line interface based on Node.js, one part of which is to download an image from a given URL using this code, taken from this SO question:

var download = function(uri, filename, callback){
  request.head(uri, function(err, res, body){
    if (err) console.trace(err);

    // Only do things if there is an image
    if (parseInt(res.headers['content-length']) > 0) {
      request(uri).pipe(fs.createWriteStream(filename)).on('close', callback);
    }
  });
}

and save it locally. The file is then opened later on by this same Node.js application.

The issue is that when the Node.js package is installed like so:

npm install -g myNodeExecutable

It can run, but it doesn't have permission to save the image in the same folder, i.e. /usr/local/lib/node_modules/myNodeExecutable/img.jpg. Is there a directory that my Node.js executable will have access to? Let me know if you need details.