How to Optimize Images for the Web: Front-End Developer’s Best Practices

Maksym Mudrenok

Maksym Mudrenok

Senior Quality Assurance Engineer

Top 5 Image Optimization Methods for a Faster Website

Ever seen a website without a single image? Probably not. They’re everywhere on the internet, right?

But images aren’t just pretty pictures for blog posts, either. We’re talking about everything from layouts and design elements to logos and profile pics.

Now, you simply can’t build a website without using them. But, as any website owner or front-end developer knows, images aren’t always easy to deal with. 

BlueCorona found that 39% of people stop engaging with a site when images take too long to load. Google considers site speed when ranking results, where image optimization plays a huge role — read our new article to learn more: How to Optimize Core Web Vitals in 2024

Besides choosing the right images and figuring out where to put them, there are technical challenges too:

These are questions we are considering today. Let’s dive into the guide on optimizing images for the web and making them look amazing on any device. Your website’s speed and user experience depend on it.

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Why does image optimization matter?

Images make websites beautiful and engaging. But here’s the thing: those lovely images come with a cost. They can take up a huge amount of space and bandwidth on your site.

Check this out: images are 51% the size of a typical web page. That’s massive. And it’s not like we can just remove images altogether.

Analyze your website content using different monitoring services like Pingdom
Source: Pingdom

So, what can we do instead? Optimize them, of course!

The benefits are huge: 

But wait, there’s more! Image optimization can also save bandwidth and storage costs.

Read more about the benefits of database optimization for the business in our latest article.

The 5 key steps to properly optimize images for a website

The goal of image optimization is to walk that fine line between having visually stunning images and lightning-fast loading times. You want your images to look their best without bogging down your website.

How do we achieve this balance?

You don’t need to be a tech whiz to start. There are many image optimization tools and plugins to help you improve your pictures with ease. We’ll delve into these in more detail later.

Choosing the appropriate image file format

There are three main options: JPEG, PNG, and GIF. Each one has its own strengths and best use cases, so choosing the appropriate format is crucial for optimizing your images for the web.

This is the go-to format for photos and other images with complex colours. They allow high quality with smaller file sizes compared to other formats.Perfect for graphics, illustrations, logos, icons. PNGs are lossless, meaning no quality is lost during compression.Limited to 256 colours, so best used for simple graphics and animated images (though video is often better for animations now).
Size of the same image in different formats
Source: National Geographic

If you’re looking to take your image optimization to the next level, check out these formats:

The key thing to remember is that each of these formats excels at different things. Photos = JPEG, graphics/transparency = PNG, animations = GIF (or video), with WebP and AVIF being solid modern alternatives.

Not sure which format is best for a particular image? Google’s PageSpeed Insights tool can analyze your images and suggest optimizations, including the ideal format. You can even download the optimized versions directly from the service.

Image compression techniques

After you’ve got your images in the right file format and properly sized, it’s time to compress them for maximum website optimization. There are two main types of compression: lossy and lossless.

Lossy compression gets rid of some image data to make the file smaller, while lossless compression reorganizes the existing data into a more compact package.

Lossy vs Lossless compression
Source: Wikipedia

For photographs and images with lots of colours/details, lossy compression is usually the way to go. It’ll shrink the file, and you likely won’t even notice the slight quality loss. But for graphics, icons, and images with fewer colours, stick to lossless so you don’t lose any important details.

Many tools are available to streamline the image compression process, here are some of the most popular.


Screenshot of the TinyPNG website homepage
Source: TinyPNG

Leveraging intelligent lossy compression, TinyPNG efficiently reduces PNG and JPEG file sizes without compromising visual quality.


Screenshot of the Optimizilla website homepage
Source: Optimizilla

This versatile online tool provides customizable compression levels, allowing users to fine-tune the balance between file size and image quality.

ImageOptim (Mac)

Screenshot of the ImageOptim for Mac website homepage
Source: ImageOptim

Combining various lossless compression techniques, ImageOptim effectively optimizes images without sacrificing quality.

FileOptimizer (Windows)

Screenshot of the FileOptimizer for Windows website homepage
Source: FileOptimizer

A versatile free tool capable of compressing various file types, including images, with both lossy and lossless options.

Resizing and cropping images

One of the easiest ways to optimize images is by resizing or cropping them before you upload them to your website. This is particularly important for large, high-resolution images from digital cameras, which often have dimensions far exceeding what’s necessary for web display.

For example, imagine your website displays blog images at 500 pixels by 500 pixels. Uploading a 1024-pixel by 1024-pixel image means all those extra pixels are adding unnecessary weight to the file, slowing down your site without any visual benefit.

You can easily resize or crop them using various editing tools, both online and offline. Popular options include GIMP or even simpler tools like Preview (Mac) or Paint (Windows).

However, when choosing the right image size, there’s more to consider than just the dimensions of the container where the image will be displayed.  

DPR (device pixel ratio) refers to the ratio between the physical pixels on a device’s screen and the logical pixels used by the operating system. For example, a device with a DPR of 2 means that each logical pixel is represented by 2 physical pixels.

Therefore, if an image is displayed in a 500-pixel by 500-pixel container on a device with a DPR of 2, the optimal image size would be 1000 pixels by 1000 pixels.

Using lazy loading

Picture this: you land on a webpage, and instead of waiting for all the images to load at once, only the ones you see immediately pop up. As you scroll down, more images magically appear, just in time for you to view them. That’s lazy loading in action.

This technique delays image loading until they’re actually needed. When a visitor first arrives on your page, only the images above the fold (the visible part of the page) are loaded. As they scroll down, the rest of the images are fetched and displayed on the fly.

Modern browsers support lazy loading through the loading=”lazy” attribute within image tags. This simplifies implementation, requiring no additional JavaScript libraries or plugins. 

However, for older browsers or more complex scenarios, JavaScript libraries like LazyLoad or yall.js offer enhanced functionality and customization options.

Responsive images

Let’s be real, your website visitors aren’t all sitting at their desks staring at huge monitors. They’re checking out your site on their phones, tablets, and maybe even their smartwatches.

The idea behind responsive images is simple. Instead of loading a single, massive image file on all devices, you provide multiple versions of each image at different sizes. Then, the browser can intelligently choose and download the perfectly sized image for that particular screen and resolution.

Your image should look good on different devices
Your image should look good on different devices. Source: The Spruce Pets

For example, you might have a large 2000px version for desktop displays, a 1000px one for tablets, and a 500px image for mobile phones. By serving the right-sized asset, you avoid wasting bandwidth on downloading unnecessary pixels while still delivering a crisp experience.

Responsive images work using the srcset and sizes attributes in your <img> tags:

<img srcset=”image-500.jpg 500w, image-1000.jpg 1000w, image-2000.jpg 2000w” sizes=”(max-width: 600px) 500px, (max-width: 1200px) 1000px, 2000px” src=”image-2000.jpg” alt=”Responsive image”>

The srcset lists the different image files and their widths. The sizes attribute describes the layout size at different viewport widths. The browser combines this info to choose the best image source for that screen size and device pixel ratio.

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The importance of descriptive Alt text

Okay, here’s the thing: search engines aren’t mind readers. They can’t actually “see” your images, so they rely on alt aka alternative text — that little description you add to your image code — to figure out what’s going on. 

Why does this matter?

Well, for starters, it helps visually impaired folks who use screen readers understand your images. But it also helps search engines index your images and figure out if they’re relevant to someone’s search query.

Here are a few tips on how to write good alt text:

Now, you might be wondering,

Do I really need to know HTML to add alt text?

Don’t worry, most website builders and content management systems have built-in tools that let you add alt text easily. Just look for the “alt text” field when you upload or insert an image.

Don’t forget to add relevant Alt to your images. How to do it on WordPress
How to add Alt text in the WordPress editor

If you’re coding your site from scratch without a visual editor, you’ll need to use HTML’s alt attribute within the image tag:

<img src=”hiking-boots.jpg” alt=”summer hiking boots – brown leather boots on a rocky trail”>

Adding alt text is a simple way to make your site more accessible and optimize images for websites for better SEO.

Wrapping up

By now, you understand just how crucial image optimization is for delivering a fast, enjoyable website experience. From speeding up load times to boosting SEO and saving bandwidth, the benefits are numerous.

The good news? Getting started is easier than you might think.

By choosing the right file formats, compressing images, resizing them appropriately, and implementing lazy loading, you can significantly reduce loading times and create a smoother browsing experience for your visitors.

Still, feeling a little lost on where to begin? No problem! The Alva experts are here to help. 

Reach out for a comprehensive SEO audit, and we’ll analyze your site’s images (along with other key factors) to identify optimization opportunities.

Want a faster, user-friendly website?

Our website audit will pinpoint exactly what’s holding you back.

A faster, more engaging website is within reach. All it takes is prioritizing visual optimization as part of your e-commerce strategy.

What are you waiting for? Request your free audit today, and let’s get to work.