If your website feels sluggish, badly optimised images are usually the first thing to blame. Optimising images for the web means choosing the right file format, compressing files without ruining quality, sizing them correctly for where they sit on the page, writing useful alt text, and loading them in a way that does not hold up everything else. Get these five things right and you will typically see faster load times, better visibility in Google, and visitors who stick around long enough to actually convert.
I have lost count of the client sites we have taken over at Flow20 where a single unoptimised hero image was adding two or three seconds to the load time on its own. That is not a small thing. As the digital marketing industry keeps growing, competition for attention gets tighter, and a slow page is often the reason someone leaves before they have even read your headline. If you are sending paid traffic through a PPC marketing agency, every second of delay is money spent sending people to a page that fails them before they convert.
Why image optimisation matters more than people think
Images are usually the heaviest files on any page. A photo straight off a phone camera can easily be 4MB or more, while a properly optimised version of the same shot might sit under 200KB with barely any visible difference. Multiply that across a page with ten or fifteen images and you can see why load times spiral. This is exactly the kind of unglamorous technical work we cover in our piece on getting the most from your SEO strategy, where the basics consistently outperform chasing the latest algorithm rumour.
Choose the right file format
Not every image belongs in the same format. JPEG suits photographs. PNG suits graphics with transparency or sharp edges, such as logos. WebP and the newer AVIF format both offer smaller file sizes than either while keeping quality high, and current browsers support them well. SVG is best for icons and simple illustrations, since it scales cleanly without losing sharpness.
| Format | Best for | Typical file size |
| JPEG | Photographs | Medium |
| PNG | Logos and transparent graphics | Large |
| WebP | Photos and graphics generally | Small |
| AVIF | Photos, where browser support allows | Smallest |
| SVG | Icons and simple illustrations | Very small |
Compress before you upload, not after
Free tools such as TinyPNG or Squoosh strip out unnecessary data with barely any noticeable drop in quality. Build the habit of compressing every image before it goes anywhere near your CMS. This single step does more for site speed than most of a typical technical SEO checklist combined.
Resize images to the space they actually fill
Uploading a 3000 pixel wide image into a container that displays at 600 pixels wastes bandwidth for no visual gain whatsoever. Resize to the real display dimensions first, then compress. This matters just as much on social creative, where a bloated image can quietly slow down the landing page that a Facebook ads agency or a LinkedIn advertising campaign sends people to.
Write alt text that actually helps someone
Alt text describes an image to search engines and to visitors using screen readers. Keep it short, accurate and free of keyword stuffing. “Woman using laptop in office” tells Google and a screen reader user exactly what is there. “Best digital marketing agency London SEO PPC” tells them nothing and reads exactly like what it is. It is worth applying the same conversion tracking mindset here that we cover in our guide to understanding LinkedIn’s conversion tracking, where the small, unglamorous details tend to be the ones that move the numbers.
Let images load only when they are needed
Lazy loading defers offscreen images until a visitor actually scrolls to them, which speeds up the initial load considerably. Most modern CMS platforms support this natively now. If you are already investing in SEO services or running a Google Ads agency campaign, this one technical fix is usually cheaper to implement than almost anything else on your list, and the impact on both rankings and conversion rate can be significant.
FAQs
Does image size affect SEO?
Yes. Large, unoptimised images slow down page load, which is a known ranking factor, and slow pages tend to increase bounce rate too.
What is the best image format for websites in 2026?
WebP is now widely supported across browsers and gives a strong balance of quality and file size for most everyday use.
How small should a web image file be?
As a general guide, aim to keep most images under 200KB. Hero images can occasionally run larger if the compression has been done properly.
If your website is losing visitors before they even see what you offer, get in touch with Flow20 and we will show you exactly where the friction is and how to fix it.
