node-gd 是 libgd 的 node binding, gd 常用于 PHP 中 … 嫌 node-canvas 的 backend cario 依赖过多可以看下这个

验证码示例 https://gist.github.com/magicdawn/f7dca2f8de039cb5b3800f1ea3fef0ff

'use strict'

const fs = require('fs')
const _ = require('lodash')
const onecolor = require('onecolor')
const gd = require('node-gd')
// https://github.com/y-a-v-a/node-gd/blob/master/docs/index.md

// Set full path to font file
const fontpath = __home + '/files/fonts/arial.ttf'

/**
 * 获取 Buffer
 */

exports.genBuffer = (function(text) {
  const width = 100
  const height = 40
  const img = gd.createSync(width, height)

  // Set background color
  img.colorAllocateAlpha(255, 255, 255, 1)

  // 验证码
  drawString(text)

  // 躁点
  drawPoints()

  // buf
  // jpeg: 0-100, 质量
  // png: 0-9
  const buf = new Buffer(img.jpegPtr(50), 'binary')
  img.destroy()
  return buf

  /**
   * draw text
   */

  function drawString() {
    let x = 10
    for (let c of text) {
      const color = randomColor()
      const size = _.random(18, 20)
      const angle = _.random(-Math.PI / 6, Math.PI / 6)
      const y = angle > 0 ? 30 : 20
      img.stringFT(color, fontpath, size, angle, x, y, c)
      x += size - 5
    }
  }

  /**
   * 躁点
   */

  function drawPoints() {
    for (let x = 0; x < 100; x += 10) {
      for (let y = 0; y < 40; y += 10) {
        img.filledEllipse(
          _.random(0, width),
          _.random(0, height),
          2, 2, // 半径
          randomColor()
        )
      }
    }
  }

  /**
   * 随机颜色
   */

  function randomColor() {
    return img.colorAllocate(
      _.random(0, 255),
      _.random(0, 255),
      _.random(0, 255)
    )
  }
})

/**
 * 获取 base64 表示
 */

exports.genBase64 = (function(text) {
  const buf = exports.genBuffer(text)
  return 'data:image/jpg;base64,' + buf.toString('base64')
})