Images make a website inviting — but they can also quietly drag it down. Heavy, unoptimised pictures are one of the most common reasons a site loads slowly, and slow sites lose both visitors and rankings. The good news is that image optimisation isn't complicated once you break it into steps, and getting it right makes your pages faster, more accessible and more visible in search (including Google Images).
- Choose the right format (WebP where you can) and compress every image before uploading.
- Use descriptive file names and alt text so search engines understand each image.
- Serve responsive images so they look sharp and load fast on every device.
- Test with Google PageSpeed Insights and keep an eye on your Core Web Vitals.
Why image optimisation matters for SEO
Image optimisation works on two fronts. Technically, smaller, well-built images load faster — and page speed is a genuine ranking factor that also keeps visitors from bouncing. Editorially, well-described images help search engines understand your content, surface your pictures in image search, and improve accessibility for people using screen readers. Done together, it's a quiet win that lifts both user experience and visibility.
The technical basics
Start with the right format
Choosing the right file format sets you up for speed. WebP is the modern all-rounder — high quality at smaller file sizes, ideal for fast loading. JPEG still works well for photos with lots of colour, and PNG is best for simple graphics or when you need transparency. Where your platform supports it, WebP is usually the smart default.
Compress without losing quality
Nobody waits around for a slow page. Compressing images shrinks their file size so your site loads quickly, and tools like TinyPNG, Squoosh or Photoshop do it without any visible drop in quality. Many platforms and plugins can also compress and convert to WebP automatically as you upload.
Serve responsive images
A picture that looks great on a desktop can be needlessly huge on a phone. Responsive images automatically serve an appropriately sized version for each screen, so a mobile visitor isn't downloading a giant desktop file. Since most browsing happens on mobile, this is one of the highest-impact fixes you can make.
SEO-focused image optimisation
Write descriptive alt text
Alt text describes an image for screen readers and tells search engines what it shows. Write it naturally — "small business owner reviewing SEO results on a laptop" beats a string of keywords — and include a relevant term only where it genuinely fits. The same clear descriptions increasingly help AI and visual search understand your content too — part of broader content creation done well.
Use meaningful file names
Search engines read file names, so rename images before uploading. "gold-coast-seo-strategy-session.jpg" tells Google far more than "IMG_0481.jpg" — a small habit that helps you turn up in image search.
Add captions where they help
Captions sit right under an image and tend to get read more than the surrounding text. They're not as critical as alt text, but where a caption adds value, it reinforces your message and gives search engines a little more context.
Consider an image sitemap and location data
If your site is image-heavy, an image sitemap helps Google discover pictures it might otherwise miss, including ones loaded by JavaScript. And for local businesses, adding geographically relevant detail to your images and their descriptions can support your local search visibility.
Test and measure your performance
You can't improve what you don't measure. Run your pages through Google's PageSpeed Insights to see how your images affect load times, and keep an eye on your Core Web Vitals — Google's metrics for speed and stability. If images are slowing you down, that report will tell you exactly where to act. The technical side of all this sits within technical SEO, where speed and page experience really pay off.
