Why image SEO matters
Three reasons:
- Performance. Images are usually the heaviest things on your pages. Optimising them is the single biggest speed win on most sites.
- Discovery. A surprising amount of search traffic comes through Google Image search, especially in visual industries like interior design, food, fashion and photography.
- Accessibility. Alt text helps screen reader users understand your content. It’s the right thing to do, and Google rewards accessible sites.
And it’s all stuff you can do yourself. No developer required.
Use the right file format
Three formats matter for the modern web:
- JPG for photographs. Smaller than PNG, perfect for anything with lots of colour and detail.
- PNG for graphics with transparency or sharp edges (logos, icons, screenshots).
- WebP for almost everything. Modern format that’s significantly smaller than JPG or PNG without losing quality. Supported by all current browsers.
If your CMS supports WebP (most modern WordPress setups do), use it as your default. Some plugins (ShortPixel, Imagify, Smush) will automatically convert your existing JPG and PNG files to WebP and serve the right one based on the visitor’s browser.
Resize before you upload
One of the most common mistakes: uploading a 4000-pixel-wide photo straight from your camera to a website that displays it at 800 pixels. The browser still has to download the full file, just to shrink it. Multiply that by every image on the page and you can see why pages get heavy.
Before uploading:
- Resize to the actual maximum dimension it will be displayed at
- Compress with a tool like TinyPNG, Squoosh or your image optimisation plugin
- Aim for under 200KB for hero images, under 100KB for inline images, under 30KB for icons
For more on speed and its impact, see why website speed matters more than you think.
Name your files properly
“IMG_4823.jpg” tells Google nothing. “lutyens-grey-kitchen-chichester.jpg” tells Google what’s in the image and where it was taken. The file name is a small but real ranking signal, and it’s free to get right.
Some rules:
- Use descriptive, lowercase, hyphenated file names
- Include relevant keywords naturally (not stuffed)
- Avoid spaces, special characters and underscores
- Be specific to the image, not generic
Write proper alt text
Alt text is what screen readers read aloud, and what shows up if the image fails to load. It’s also a major signal Google uses to understand the image. Most sites either skip alt text completely or use generic phrases like “image” or “photo”.
Good alt text:
- Describes what’s actually in the image
- Includes relevant keywords naturally where they fit
- Is short (a sentence or two)
- Doesn’t start with “Image of…” (screen readers already know it’s an image)
- Is left blank (‘alt=””‘) for purely decorative images, so screen readers skip them
Examples:
- Bad: alt=”kitchen.jpg”
- Mediocre: alt=”grey kitchen”
- Good: alt=”Modern grey kitchen with marble worktops in a Chichester family home”
Use captions where they help
Captions are read by users far more than body text. If you’ve got a portfolio image or a photo that supports a key point, a caption is a natural opportunity to add context, keywords and a small ranking boost.
Don’t caption everything, though. Captioning every image clutters the page. Use captions where they genuinely help the reader understand what they’re looking at.
If you only do one thing for image SEO, do this: rename your most important images and add real alt text. Twenty minutes of work, lasting impact.
These same image checks, descriptive file names, real alt text and compressed files, are built into our SEO and AI content checklist so they become part of publishing every page.
Lazy load images below the fold
Lazy loading means images further down the page don’t download until the visitor scrolls towards them. This dramatically reduces initial page weight and improves Largest Contentful Paint, which we covered in Core Web Vitals explained.
WordPress now lazy-loads images by default in modern versions. If you’re on something else, your developer or theme can usually enable it with a single setting.
Set explicit width and height
Always tell the browser the dimensions of your images in the HTML. Without that, the browser has to guess, and the layout often jumps around as images load. This hurts Cumulative Layout Shift, which Google measures as part of Core Web Vitals.
Most modern CMS platforms do this automatically when you insert an image. If yours doesn’t, ask your developer to add it.
Image sitemaps and structured data
For sites where images are central to the offering (portfolios, recipe sites, online shops, photography), it’s worth submitting an image sitemap and adding ImageObject schema to your important images. This helps Google index them properly and consider them for image search.
Most SEO plugins (Rank Math, Yoast) handle the sitemap automatically. Schema is also handled by most modern plugins for common content types.
Common mistakes to avoid
- Stuffing alt text with keywords. alt=”cheap kitchen affordable kitchen new kitchen kitchen ideas” is spam. Google ignores it and screen readers hate it.
- Using the same alt text across many images. Each image deserves its own description.
- Embedding important text inside images. Search engines can’t read it, screen readers can’t read it. Use real text.
- Slideshows with massive uncompressed images. A common cause of slow homepages.
- Using stock photos that look obviously like stock. Bad for trust, also bad for image SEO because they exist on hundreds of other sites.
For more on trust signals (which include real photography), see trust signals: the small details that influence buying decisions.
A simple image SEO audit you can do this week
- Pick your five most important pages.
- For each image on each page, check: file name, file size, alt text, dimensions.
- Rename anything generic.
- Add alt text where it’s missing.
- Compress anything over 200KB.
- Resize anything bigger than the displayed dimensions.
- Test the page in PageSpeed Insights before and after.
You’ll usually see a measurable improvement in performance scores immediately, and the SEO benefits build up over the following weeks.
For platforms that make it easier
If you’re on WordPress, plugins like ShortPixel, Imagify, EWWW Image Optimizer or Smush will handle compression and WebP conversion automatically. They’ll even retroactively process every image you’ve already uploaded.
If you’re on Shopify, Squarespace or Wix, image optimisation is mostly built in, but you should still resize before uploading and write your own alt text. The platforms can’t write descriptions for you.
Small effort, ongoing payback
Image SEO is one of the few areas where the work compounds quietly. Every well-named, well-optimised image makes your site a little faster, a little more accessible, and a little more visible. Do it for new images as you upload them, and gradually fix the worst offenders on your existing pages. Within a few months, your whole site is in better shape.
If you’d like a hand auditing the images on your site (especially if you’ve got a portfolio-heavy site that’s slow), get in touch. It’s one of the cheapest, fastest improvements we can run.
