Simple Image Optimiser: optimise images for SEO without Photoshop.

Images are the single biggest cause of slow websites — and slow websites don't rank. But getting image optimisation right doesn't require Photoshop, a degree in web development, or an hour of your afternoon. It requires knowing three things: the right file size, the right format, and the right metadata.

This is the practical guide we wrote for our clients — and the reason we built imageoptimiser.io, a free browser-based tool that handles the technical side in about thirty seconds.

Why image optimisation is an SEO issue.

Google's ranking algorithm has included page speed as a factor since 2010, and the introduction of Core Web Vitals in 2021 made it impossible to ignore. Largest Contentful Paint (LCP) — one of the three Core Web Vitals — is almost always determined by the largest image on a page. If that image is heavy and slow to load, your LCP score suffers, your rankings suffer, and your bounce rate climbs.

Google recommends keeping images under 100KB for optimal performance, with 200KB as an absolute maximum. Most images straight off a camera or phone are between 3MB and 8MB — thirty to eighty times too large. A single unoptimised hero image can add two to four seconds to your page load. That's enough to push visitors away before your page has finished appearing.

Image SEO isn't just about file size, though. It includes the format you use, how you name your files, the alt text you write, and the dimensions you set. Get all of those right, and images become an asset for your SEO rather than a liability.

Image optimisation best practices.

1. Use WebP format.

WebP is the format Google developed specifically for the web. It produces file sizes 25–35% smaller than JPEG at equivalent quality, and 25–50% smaller than PNG. All modern browsers support it, and Google recommends it explicitly in its image SEO guidance. If you're still saving images as JPEGs or PNGs without converting them, you're leaving performance on the table.

2. Keep images under 100KB.

For most website images — blog post headers, team photos, product images, service page images — 100KB is the target. Background images or full-width hero images can stretch to 150–200KB, but anything beyond that starts to drag. The smaller the file, the faster the page, the better the Core Web Vitals score.

3. Set the right dimensions.

There's no point uploading a 4000px-wide image for a blog post that displays at 800px. The browser downloads the full file regardless of how small it renders on screen. Set your width to match the largest size the image will actually appear on your site. For a standard blog post image, 1200px wide is usually more than enough. For thumbnails, 600–800px is typically sufficient.

4. Name your image files properly.

Image file name SEO is often overlooked but genuinely matters. Google reads image filenames as a signal for what the image contains. A file named IMG_3847.jpg tells Google nothing. A file named ai-automation-services-london.webp tells Google exactly what the image is — and when that matches your page keywords, it reinforces your relevance.

Use lowercase, hyphens between words (not underscores), and include your primary keyword where it naturally fits. Keep it descriptive but concise.

5. Write descriptive alt text.

Alt text serves two purposes: accessibility (screen readers use it to describe images to visually impaired users) and SEO (search engines use it to understand image content). Good alt text is a concise, accurate description of what the image shows — not a list of keywords crammed together.

For a photo of a website design mockup: Website design mockup for a London estate agent — not website design web design london web development agency. Google is very good at detecting keyword stuffing in alt text, and it penalises it.

Alt text best practices in short: be accurate, be specific, include your keyword where it fits naturally, and keep it under 125 characters.

6. Consider lazy loading.

Lazy loading tells the browser to only load images when they're about to scroll into view, rather than loading the entire page upfront. It's a simple addition to your image tags (loading="lazy") that can meaningfully reduce initial page load time — particularly on image-heavy pages. The exception is your above-the-fold image (the first thing visible on load) — that should use loading="eager" to ensure it appears immediately.

Why we built imageoptimiser.io.

Almost every client we work with — from small business owners updating their own blog posts to marketing teams managing content across multiple sites — hits the same wall: they know their images need optimising, but they don't want to buy and learn Photoshop or subscribe to another tool they'll use once a month.

So we built imageoptimiser.io: a free, browser-based image optimisation tool that handles resizing, compression, and format conversion in about thirty seconds. No account needed. No subscription. No files uploaded to a server — everything is processed directly in your browser, so your images never leave your device.

You set your target width, choose WebP (or JPEG or PNG), set a max file size, and drop your images in. It processes them instantly and gives you a download button. That's it.

How to use it: four steps.

1. Configure — Set your target width (1200px works for most blog images), choose WebP as your output format, and set a max file size — 100KB is a good default for web images.
2. Upload — Drag and drop your images or click to browse. You can process multiple files at once, which makes it fast if you're preparing a batch of images for a new page or blog post.
3. Process — Click the Process button. It runs instantly in your browser with no waiting, no uploading, and no server involved.
4. Download — Download your optimised images individually or click "Download All" to grab the whole batch as a zip file.

The tool handles crop strategy too — you can choose to keep the aspect ratio, or crop from the centre, top, or bottom if you need a specific height. For more complex cropping, Windows Photos or Mac Preview both have free built-in crop tools that take about ten seconds to use.

Image SEO is part of a bigger picture.

Getting your images right is one piece of a well-optimised website. The others — page structure, Core Web Vitals, crawlability, internal linking, metadata — all contribute to how Google understands and ranks your site. Image compression SEO alone won't rescue a poorly structured site, but it will meaningfully improve a well-built one.

If you're building or redesigning a website and want SEO baked in from the start rather than bolted on afterwards, that's where our website design service comes in. Every site we build is optimised for performance and search from the ground up — proper image handling, Core Web Vitals, structured data, and a CMS that makes it easy to keep things that way.

For ongoing SEO and AEO — including image SEO audits, technical fixes, and content strategy — our SEO & AEO service covers the full picture. And if you're thinking about AI-powered content workflows that include image handling as part of a broader automation, our AI transformation service is worth a look.

The image optimisation checklist.

Before you publish any image, run through this:

• File size under 100KB (200KB maximum for large hero images)
• Format: WebP where possible; JPEG for photos if WebP isn't an option
• Dimensions match the largest size the image will display at
• Filename is descriptive, lowercase, hyphenated, and includes your primary keyword
• Alt text is accurate, descriptive, and under 125 characters
• Above-the-fold image uses loading="eager"; all others use loading="lazy"

That's the complete image SEO checklist. Run your images through imageoptimiser.io before you upload them, fill in your alt text, name your files properly, and you've done more than most websites bother to do.