Improving WordPress Image Handling

Paul Littlewood
12 Dec 2021
  • PHP
  • Wordpress

In the last decade, desktop page weight has increased by 221% (2,315 KB in June 2022) and mobile page weight has increased by a whopping 594% (2,020 KB in June 2022). It’s clear that page loading time affects user experience, especially on slower mobile connections. However, many overlook the environmental impact of storing and transmitting all this data. Data centres require energy to operate, and this is becoming a major issue. As the Sustainable Web Manifesto states, “If the Internet were a country, it would be the sixth largest polluter.”

Images account for roughly 50% of a web page’s size, making them the most obvious place to start optimising.

Wasteful WordPress

WordPress has some major issues with how it handles images. Upload an image to a fresh installation and seven scaled versions of that image are automatically created on your server. The idea is that your theme can use these scaled versions (or thumbnails), to display the right size images in different parts of the template. However, the system does not discriminate when generating thumbnails; it creates all defined thumbnail sizes for every image, even if they are obviously unnecessary and will never be used.

The issue gets worse when plugins are installed, as they often introduce their own custom thumbnail sizes. For example, WooCommerce adds three new image sizes, which are applied not just to product images, but to all images on the website. Those familiar with WordPress will know how quickly the wp-content folder can become cluttered with unnecessary images, most of which will never be used. With 63.5% of all websites on the internet running WordPress, the sheer amount of storage space and energy wasted by such an inefficient system is inexcusable.

Responsive Images

WordPress also uses these scaled images in its responsive image solution. The idea being that it can co-opt these thumbnails for responsive design by lumping them all in a srcset. This is a misguided and lazy idea approach, as the thumbnail sizes chosen by a theme are very unlikely to also be efficient choices for generating a srcset suitable for serving efficiently sized images to different types of device.

An Alternative Approach: Images on Demand

An alternative to generating all these images is to only generate an image only when it is needed. This may sound slow, but luckily there are image management services such as imgIX, ImageKit and Cloudinary that can help. These services can generate a scaled version of an image, convert it to an optimal format (e.g., WebP), and serve it from a location close to the user via their content delivery network (CDN) in a fraction of a second. After the initial image generation, it becomes even quicker for subsequent users, who can now download a cached version.

But how do we integrate these services with WordPress as an alternative thumbnail and responsive image solution?

WordPress Images on Demand Plugin

Images on Demand is a WordPress plugin that provides an alternative way of serving scaled images by integrating with an image CDN. It replaces both the native WordPress thumbnail and responsive images functionality. This helps to save server space and improve page load speed compared to the default WordPress approach.

Responsive Images

  • Generates an image srcset based on the dimensions of the original image, using a customisable algorithm to determine the dimensions for each image in the srcset.
  • Generates a sizes attribute (using lazysizes) to help the browser select an appropriate image size to download.
  • Integrates with your image CDN to generate and serve the scaled images.


  • Prevents the generation of default WordPress thumbnails.
  • Replaces WordPress thumbnails with scaled image from CDN.