index.js

const { parse } = require('url')
const rp = require('request-promise')
const pixelmatch = require('pixelmatch')
const sizeOf = require('image-size')

module.exports = async (req, res) => {
  const { query } = parse(req.url, true)
  const { image_url, other_image_url } = query

  if (
    typeof query == 'undefined' ||
    typeof image_url == 'undefined' ||
    typeof other_image_url == 'undefined'
  ) {
    res.end('USAGE: set image_url and other_image_url as query params')
  } else {
    const image = await rp(image_url, { encoding: null })
    const other_image = await rp(other_image_url, { encoding: null })

    const image_size = sizeOf(image)
    const other_image_size = sizeOf(other_image)

    const pixel_difference = pixelmatch(
      image,
      other_image,
      null,
      image_size.width,
      image_size.height
    )

    const percent_difference = (pixel_difference / (image_size["width"] * image_size["height"])) * 100.0

    const results = {
      image: image_size,
      other_image: other_image_size,
      pixel_difference: pixel_difference,
      percent_difference: Math.round(percent_difference * 10) / 10
    }

    res.end(JSON.stringify(results))
  }
}