Drew McLellan draws this, our fourteenth season to a gentle close by getting a little Inside Snowball and gives an account of how we put the robots to work in generating custom dynamic social media sharing images for each of the articles here on the site. Christmas is a time to share what you have, even if it’s just a grid of pixels.


Way back when social media was new, you could be pretty sure that whatever you posted would be read by those who follow you. If you’d written a blog post and you wanted to share it with those who follow you, you could post a link and your followers would see it in their streams. Oh heady days!

With so many social channels and a proliferation of content and promotions flying past in everyone’s streams, it’s no longer enough to share content on social media, you have to actively sell it if you want it to be seen. You really need to make the most of every opportunity to catch a reader’s attention if you’re trying to get as many eyes as possible on that sweet, sweet social content.

One of the best ways to grab attention with your posts or tweets is to include an image. There’s heaps of research that says that having images in your posts helps them stand out to followers. Reports I found showed figures from anything from 35% to 150% improvement from just having image in a post. Unfortunately, the details were surrounded with gross words like engagement and visual marketing assets and so I had to close the page before I started to hate myself too much.

So without hard stats to quote, we’ll call it a rule of thumb. The rule of thumb is that posts with images will grab more attention than those without, so it makes sense that when adding pages to a website, you should make sure that they have social media sharing images associated with them.

Adding sharing images

The process for declaring an image to be used in places like Facebook and Twitter is very simple, and at this point is familiar to many of us. You add a meta tag to the head of the page to point to the location of the image to use. When a link to the page is added to a post, the social network will fetch the page, look for the meta tag and then use the image you specified.

<meta property="og:image" content="https://example.com/my_image.jpg">

There’s a good post on this over at CSS-Tricks if you need to bone up on the details of this and other similar meta tags for social media sharing.

This is all fine and well for content that has a very obvious choice of image to go along with it, but what if you don’t necessarily have an image? One approach is to use stock photography, but that’s not going to be right for every situation.

This was something we faced with 24 ways in 2017. We wanted to add images to the tweets we post each day announcing a new article. Some articles have images, but not all, and there tended not to be any consistency in terms of imagery from one article to the next. We always have an author photograph, but those don’t usually lend themselves directly to being the main ‘hero’ image for an article.

Putting his thinking cap on, Paul came up with a design for an image that used the author photo along with a quote extracted from the article.

Sharing image from a 2017 article.
One of the hand-made sharing images from 2017

Each day we would pick a quote from the article, and Paul would manually compose an image to be uploaded to the site. The results were great, but the whole process was a bit too labour intensive and relied on an individual (Paul) being available each day to do the work. I thought we could probably improve this.

Hatching a new plan

One initial idea I came up with was to script the image editor to dynamically build a new image by pulling content from our database. Sketch has plugins available to pull JSON content into a design, and our CMS can easily output JSON data, so that was one possibility.

The more I thought about this and how much I wish graphic design tools worked just a little bit more like CSS, the obvious solution hit me. We should just build it with CSS!

In fact, as the author name and image already exist in our CMS, and the visual styling is based on the design of the website, couldn’t this just be another page on the site generated by the CMS?

Breaking it down, I figured the steps needed would be something like:

  1. Create the CSS to lay out a component that could be turned into an image
  2. Add a new field to articles in the CMS to hold a handpicked quote
  3. Build a new article template in the CMS to output the author name and quote dynamically for any article
  4. … um … screenshot?

I thought I’d get cracking and see if I could figure out the final steps later.

Building the page

The first thing to tackle was the basic HTML and CSS to lay out the components for our image. That bit was really easy, as I just asked Paul to do it. Everyone should have a Paul.

Paul’s code uses a fixed dimension container in the HTML, set to 600 × 315px. This is to make it the correct aspect ratio for Facebook’s recommended image size. It’s useful to remember here that it doesn’t need to be responsive or robust, as the page only needs to lay out correctly for a screenshot and a fixed size in a known browser.

With the markup and CSS in place, I turned this into a new template. Our CMS can easily display content through any number of templates, so I created a version of the article template that was totally stripped down. It only included the author details and the quote, along with Paul’s markup.

I also added the quote as a new field on the article in the CMS, so each ‘image’ could be quickly and easily customised in the editing process.

A screenshot of a CMS edit field
I added a new field to the article template to capture the quote.

With very little effort, we quickly had a page to dynamically generate our ‘image’ right from the CMS. You can see any of them by adding /sharing onto the end of an article URL for any 2018 article.

Sharing image from a 2018 article.
Our automatically generated layout direct from the CMS

It soon became clear that the elusive Step 4 was going to be the tricky part. I can create a small page on the site that looks like an image, but how should I go about turning it into one? An obvious route is to screenshot the page by hand, but that’s going back to some of the manual steps I was trying to eliminate, and also opens up a possibility for errors to be made. But it did lead me to the thought… how could I automatically take a screenshot?

Enter Puppeteer

Puppeteer is a Node.js library that provides a nice API onto Headless Chrome. What is Headless Chrome, you ask? It’s just a version of the Chrome browser than runs from the command line without ever drawing anything to a user interface window. It loads pages, renders CSS, runs JavaScript, pretty much every normal thing that Chrome on the desktop does, but without a clicky user interface.

Headless Chrome can be used for all sorts of things such as running automated tests on front-end code after making changes, or… get this… rendering pages that can be used for screenshots. The actual process of writing some code to control Chrome and to take the screenshot is where Puppeteer comes in. Puppeteer puts a friendly layer in front of big old scary Chrome to enable us to interact with it using simple JavaScript code running in Node.

Using Puppeteer, I can write a small script that will repeatably turn a URL into an image. So simple is it to do this, that’s it’s actually Puppeteer’s ‘hello world’ example.

First you install Puppeteer. It downloads a compatible headless browser (actually Chromium) as a dependancy, so you don’t need to worry about installing that. At the command line:

npm i puppeteer

Then save a new file as example.js with this code:

const puppeteer = require('puppeteer');

(async () => 
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://example.com');
  await page.screenshot(path: 'example.png');
  await browser.close();
)();

and then run it using Node:

node example.js

This will output an image file example.png to disk, which contains a screenshot of, in this case https://example.com. The logic of the code is reasonably easy to follow:

  1. Launch a browser
  2. Open up a new page
  3. Goto a URL
  4. Take a screenshot
  5. Close the browser

The async function and await keywords are a way to have the script pause and wait for normally asynchronous code to return before proceeding. That’s useful with actions like loading a web page that might take some time to complete. They’re used with Promises, and the effect is to make asynchronous code behave as if it’s synchronous. You can read more about async and await at MDN if you’re interested.

That’s a good proof-of-concept using the basic Puppeteer example. I can take a screenshot of a URL! But what happens if I put the URL of my new special page in there?

A screenshot with our page jammed in the top left corner of a big white page.
Our content is up in the corner of the image with lots of empty space.

That’s not great. It’s okay, but not great. It looks like that, by default, Puppeteer takes a screenshot with a resolution of 800 × 600, so we need to find out how to adjust that. Fortunately, the docs aren’t the worst and I was able to find the page.setViewport() method pretty easily.

const puppeteer = require('puppeteer');

(async () => 
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto('https://24ways.org/2018/clip-paths-know-no-bounds/sharing');
  await page.setViewport(
    width: 600,
    height: 315
  );
  await page.screenshot(path: 'example.png');
  await browser.close();
)();

This worked! The screenshot is now 600 × 315 as expected. That’s exactly what we asked for. Trouble is, that’s a bit low res and it is nearly 2019 after all. While in those docs, I noticed the deviceScaleFactor option that can be passed to page.setViewport(). Setting that to 2 gives us an image of the same area of the screen, but with twice as many pixels.

  await page.setViewport(
    width: 600,
    height: 315,
    deviceScaleFactor: 2
  );

Perfect! We now have a programmatic way of turning a URL into an image.

Improving the script

Rather than having a script with a fixed URL in it that outputs an image called example.png, the next step is to make that a bit more dynamic. The aim here is to have a script that we can run with a URL as an argument and have it output an image for that one page. That way we can run it manually, or hook it into part of our site’s build process to automate the generation of the image.

Our goal is to call the script like this:

node shoot-sharing-image.js https://24ways.org/2018/clip-paths-know-no-bounds/

And I want the image to come out with the name clip-paths-know-no-bounds.png. To do that, I need to have my script look for command arguments, and then to split the URL up to grab the slug from it.

// Get the URL and the slug segment from it
const url = process.argv[2];
const segments = url.split('/');
// Get the second-to-last segment (the slug)
const slug = segments[segments.length-2];

We can then use these variables later in the script, remembering to add sharing back onto the end of the URL to get our dedicated page.

(async () => 
  const browser = await puppeteer.launch();
  const page = await browser.newPage();
  await page.goto(url + 'sharing');
  await page.setViewport(
    width: 600,
    height: 315,
    deviceScaleFactor: 2
  );
  await page.screenshot(path: slug + '.png');
  await browser.close();
)();

Once you’re generating the image with Node, there’s all sorts of things you can do with it. An obvious step is to move it to the correct location within your site or project.

You can also run optimisations on the file. I’m using imagemin with pngquant to reduce the file size a little.

const imagemin = require('imagemin');
const imageminPngquant = require('imagemin-pngquant');

await imagemin([slug + '.png'], 'build', 
  plugins: [
    imageminPngquant(quality: '75-90')
  ]
);

You can see the completed example as a gist.

Integrating it with your CMS

So we now have a command we can run to take a URL and generate a custom image for that URL. It’s in a format that can be called by any sort of build script, or triggered from a publishing hook in a CMS. Exactly how you do that is going to depend on the way your site is built and the technology stack you’re using, but it’s likely not too hard as long as you can run a command as part of the process.

For 24 ways this year, I’ve been running the script by hand once each article is ready. My script adds the file to a git repo and pushes to a deployment remote that is configured to automatically deploy static assets to our server. Along with our theme of making incremental improvements, next year I’ll look to automate this one step further.

We may also look at having a few slightly different layouts to choose from, so that each day isn’t exactly the same as the last. Interestingly, we could even try some A/B tests to see if there’s any particular format of image or type of quote that does a better job of grabbing attention. There are lots of possibilities!


By using a bit of ingenuity, some custom CMS templates, and the very useful Puppeteer project, we’ve been able to reliably produce dynamic social media sharing images for all of our articles. In doing so, we reduced the dependancy on any individual for producing those images, and opened up a world of possibilities in how we use those images.

I hope you’ll give it a try!


About the author

Drew McLellan is a developer and content management consultant from Bristol, England. He’s the lead developer for the popular Perch and Perch Runway content management systems, and public speaking portfolio site Notist. Drew was formerly Group Lead at the Web Standards Project, and a Search Innovation engineer at Yahoo!. When not publishing 24 ways, he keeps a personal site about web development, takes photos, tweets a lot and tries to stay upright on his bicycle.

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Drew McLellan draws this, our fourteenth season to a gentle close by getting a little Inside Snowball and gives an account of how we put the robots to work in generating custom dynamic social media sharing images for each of the articles here on the site. Christmas is a...