If you don’t know it yet, then it’s about time you find out: The speed with which your web pages load is crucial to the success of your website or app.

In fact, just a 0.1-second improvement in mobile site speed can improve conversions by up to 10%. Not to mention that page performance is now a major search engine ranking factor.

And, in the age of global interconnectedness, there is no better tool to help improve your performance than a CDN. Currently, images make up the majority of bytes for most website pages, which means using an image CDN can deliver the most significant performance improvement.

But, what are the major similarities and differences between traditional and image CDNs? And, what’s the proof that image CDNs can deliver even better performance? Let’s find out.

Why do you need a CDN to begin with?

In the traditional model of the web, each website or domain’s content is hosted on a single physical server. This “content” includes everything that makes up the web application, from the markup files to web fonts to media assets (images, videos, audio files, etc.) to the JavaScript and CSS files.

However, the internet itself consists of a countless number of servers or nodes located all across the world and connected by global network infrastructure.

When user A visits website B, the fastest route is calculated from the server closest to A to the server where B is hosted. Depending on the geographic location and distance between both, it may take multiple “hops” between intermediary servers for requests to travel from user A to website B, and vice versa.

If you host your website from a server in New York, let’s say, and you’re visited by an internet user also in New York, good news! It will, most likely, only take a couple of hops for messages to travel between them and your website.

However, if the visitor is from somewhere in central Africa, their request, and the subsequent response, will have a much longer and more complicated route to travel. So, even if they were to click a link to your website at exactly the same time, the visitor in New York will see results much faster. While this is true for all types of content, the difference is more pronounced for larger file sizes, such as images and videos.

This is a problem because anyone with an online presence, whether it’s brands, entrepreneurs, influencers, bloggers, or retailers, is increasingly catering to a global audience.

What do we mean by a traditional CDN?

A content delivery network, or CDN, is a solution to this problem. In simple terms, a CDN utilizes multiple servers all across the globe, also called nodes, PoPs (points of presence), or edge servers. When activating a CDN for a website or app, it makes and stores copies of these files across these geographically distributed PoPs.

If we take the example above, but the website owner has subscribed to a CDN, one copy of their entire website could be stored in a server in New York and another copy in a server somewhere in Africa.

Both the visitor in New York and the one in Africa will only need to communicate with the server closest to them to request and download the files that make up the website. The same goes for any other user, anywhere else in the world, that’s also located close to one of these PoPs.

The result is faster data flow, thanks to simplifying and shortening the path between information and the viewer.

However, many traditional CDNs today also offer additional benefits, such as:

  • Enhanced security: Through features like advanced TLS/SSL encryption, Web Application Firewall (WAF), and DDoS protection.
  • Reliability & Availability: Thanks to fault-resistant infrastructure with redundancy, disaster recovery, and fall-back measures built-in. CDNs can help your website handle traffic spikes with load balancing infrastructure, for example.
  • Analytics & Reports: As they handle much of the traffic to-and-from your website, many CDNs allow you to better monitor and collect data points on your traffic.

What is an Image CDN?

Luckily, you don’t have to do any mental acrobatics to figure out what an image CDN does. In principle, an image CDN works just like an ordinary CDN with one main difference: it focuses on delivering your image files.

It uses the exact same concept of geographically arranged data centers that store copies of your files and serve them to the nearest visitors to your site. This speeds up the delivery of your image assets just like a CDN accelerates the delivery of your website files.

However, today’s top image CDNs also use a range of other techniques to further optimize your image assets to improve performance. How? Read on to find out.

Why You Should Use an Image CDN

So, the main reason you would typically be interested in a CDN is to optimize your website performance. However, did you know that images are the most important element to optimize if you want to improve your website performance?

Typically, images make up around 50% of a web page’s total payload. That’s the same, or more, than all of the markup, JS, CSS, videos, animations, web fonts, and other assets combined. According to HTTPArchive, images bytes average almost 1 MB per page, and are rising.

Google themselves has stated that images offer the greatest opportunity to improve performance for most web pages. And, even recommend image CDNs as the best way to achieve that goal.

By using a variety of optimization techniques, image CDNs can reduce image payloads by as much as 80%.

For most web pages, that translates roughly to a payload reduction that’s 50% more significant than that of a conventional CDN.

However, you can’t simply compress the heck out of your images. Low-quality images can come across as tacky, unprofessional, and unattractive which will hurt your user experience. For example, 83% of online shoppers indicated that photos are influential in their decision to buy a product. So, you need a strategy that delivers optimal performance while maintaining visual quality.

All you need to do for an image CDN to work is to supply it with the location where your images are stored on the web. The CDN will then pull these images and store copies of them across its CDN.

Whenever a visitor loads a web page with images or requests an image from your website, the image CDN will step in. Typically using the ACCEPT header, the CDN will acquire some basic information of the device the visitor is accessing your images from. More advanced image CDNs can also use client hints for even more informed decision-making.

The CDN will then either generate a new version or select an existing version of the image based on what would deliver the optimal performance.

So, how does an image CDN achieve such impressive payload savings? By doing all of the following for each of your image assets:

  • Resize your images according to the device screen size. For example, larger image versions for desktops and smaller ones for tablets or mobile devices. Or, super high-res images for Retina displays. Most image CDNs do this by using responsive syntax.
  • Intelligently compress the quality of the image to reduce the payload while preserving visual quality. Image CDNs can use advanced machine learning and AI capabilities to do this as well as calibrate image quality using metrics like the Structural Similarity Index Method (SSIM).
  • Using optimal, next-gen image formats. Different image formats can encode the same amount of visual quality in more payload-efficient ways. For example, without downgrading the quality, WebP versions of JPEG images render about 40% faster.
  • Provide directives that users can use to manually make changes to how images are optimized. For example, using simple PATH syntax in your URL, you can set the compression level to be more or less aggressive.

The key here is that an image CDN does all of this dynamically. It makes the best decision regarding how to serve optimized images on the fly based on the changing properties of each individual website visitor. Another key advantage of an image CDN is that it can deliver optimal performance without the need for much manual intervention.

Other image optimization techniques, like responsive syntax, image editing, etc. are too static in their approach and lack this automated, intelligent decision-making. This means they are also much more labor-intensive and you need to keep updating all your image assets whenever you add more images or as standards change.

The Problem With Most Image CDNs

So, yes, image CDNs are one of the best ways to boost the performance of your website. However, most image CDNs today have a crucial flaw.

When it comes to dynamically resizing images, most image CDNs require a small JavaScript applet or plugin. While it’s nothing major, it introduces some performance overhead to your pages. Not only may it impact key user-centric performance metrics, like your FID (First Input Delay) but it will also break browser pre-loading to some extent.

You will also be flagged for render-blocking resources using performance tools like Lighthouse or PageSpeed Insights.

Similarly, these CDNs typically use JavaScript-based lazy-loading which has the same issue.

ImageEngine: The Next-gen Image CDN

While there are many image CDNs on the market today, there is only one that can dynamically resize images without needing a JS applet (as far as I’m aware). And, it’s called ImageEngine.

While it works just like other image CDNs, ImageEngine also utilizes WURFL device detection. ImageEngine uses this technology to accurately identify mobile devices, like tablets and mobile phones. This gives ImageEngine more information to work with when optimizing image assets.

For example, ImageEngine can obtain the exact screen resolution, dimensions, and pixels per inch (PPI) of any device accessing your images.

The main benefit of ImageEngine is that it can use these parameters to also dynamically serve perfectly resized images without responsive syntax or JavaScript – something no other mainstream image CDN can do. Whereas typical responsive syntax is limited to 3 or 4 different image size breakpoints, ImageEngine has no such limitations.

This logic is also built into each of ImageEngine’s “device-aware edge servers.” With 20 PoPs in 18 regions, this means that decision-making takes place as close to the user as possible, improving latency and loading times.

What’s more, ImageEngine also has some of the most wide-ranging support for next-gen image formats. While WebP is pretty commonplace, very few image CDNs support JPEG 2000 (JP2) for Safari browsers. ImageEngine was also one of the first to provide support for AVIF, currently the gold standard in next-gen image formats.

ImageEngine also automatically optimizes animated GIFs (aGIFs) by serving them in the MP4 format. And, you can even use ImageEngine to accelerate the delivery of other static files.

ImageEngine also supports both client hints and the save-data:on header – something that’s not a given when it comes to most other image CDNs.

This all means that ImageEngine can reduce image payloads by more than conventional image CDNs, without a perceptible dip in visual quality. This is especially true for mobile devices, where properly resizing images can deliver huge performance benefits. With the majority of internet activity taking place on mobile devices, this means ImageEngine can give you a significant advantage in this market.

Conclusion: When Should You Use an Image CDN

So, to recap:

  • Website performance is pivotal when it comes to the overall success of your website.
  • CDNs are one of the best tools for this because it improves the performance and user experience for visitors all across the world.
  • Attractive images are also important for a website’s success but can slow down your pages as it accounts for 52% of all page weight.
  • Image CDNs can provide the same benefits as traditional CDNs, plus reduce image payloads by up to 80%.
  • Overall, this means that image CDNs can reduce payloads by up to 50% more than conventional CDNs and have a bigger positive impact on overall website performance.

With that in mind, here are the reasons why you should use an image CDN:

  • You are hoping to attract and convert a global audience or grow your online presence internationally.
  • You have a traffic-heavy website or one that is prone to experience traffic spikes.
  • You use a significant number of images on your website or need to serve many high-quality images. Or, you regularly add new images to your website.
  • You want to benefit from the extra availability and security that a CDN can offer.
  • You want to avoid spending time and resources on manually optimizing images as part of your media pipeline and conducting regular maintenance.
  • A large portion of your audience is mobile internet users.
  • An image CDN can integrate with a traditional CDN, giving you the best of both worlds, ImageEngine included.

Thanks to its unique device detection capabilities, ImageEngine is the market leader when it comes to optimizing image assets for performance. This is especially true in a mobile-dominated internet market where the variety of different devices is growing by the day.

More articles you may be interested in.


>