code: async function main(inputFile, outputFile) {
    const Canvas = require('canvas');
    outputFile = outputFile || 'out.png';
    const faces = await detectFaces(inputFile);
    console.log('Highlighting...');
    await highlightFaces(inputFile, faces, outputFile, Canvas);
    console.log('Finished!');
  }
docs: Run the example [START vision_face_detection_tutorial_run_application]