var screencapture = require('screencapture')

screencapture(function (err, imagePath) {
  // then you have imagePath as png.
  //
  // When an user exits screencapture without taking a screenshot,
  // imagePath == null
})

screencapture('/path/to/output.png', function (err, imagePath) {
  // imagePath is '/path/to/output.png' or null
})