Open the images folder of almost any website and you'll find names like IMG_4821.jpg, final-photo-2.png, or screenshot.webp. These are photos that probably weigh several megabytes, tell Google nothing about what they show, and on top of that, are slowing down the page load without anyone noticing. Image SEO is probably the easiest area to improve, and the most ignored, in all of search optimisation.
The first and simplest fix: the file name
Before you upload a photo to your site, rename it. "IMG_4821.jpg" tells Google nothing. "folding-electric-bike-black.jpg" tells it exactly what's in the image, in the same language someone would use to search for it. It's a fifteen-second fix that, multiplied across the hundreds of images a product catalogue can have, makes a real difference in how many of those images show up when someone searches Google Images.
Use words separated by hyphens, describing what's actually visible rather than what you'd like to sell. "mens-running-shoes-blue.jpg" works; "unmissable-shoe-deal.jpg" says nothing about the actual content of the image.
Alt text: not a trick, a description
The alt attribute on an image was born for accessibility: it's what a screen reader reads to a blind user to explain what image is there, and it's what shows if the image fails to load. Google uses it the same way, as its primary source of information about an image's visual content, because (unlike a person) it doesn't "see" the photo perfectly, it relies on the context you give it.
The right way to write it is to describe the image the way you'd describe it to someone over the phone: "Modern white and wood kitchen with a central island" is a good alt text. "Kitchen, kitchen remodel, cheap kitchen remodel, kitchen remodel quote" is keyword stuffing, and Google identifies it and penalises it instead of rewarding it. One image, one honest description; there's no need to cram the keyword in by force.
Format and file size: this is where speed gets lost
Images are usually, by far, the heaviest element on a web page. A single uncompressed photo from a modern camera can weigh 5, 8, or 10 megabytes; on a website, that translates into several extra seconds of load time on a normal mobile connection.
- Use WebP. It's a modern format that achieves nearly identical visual quality to JPG or PNG at a much lower file size (often 25% to 50% lighter). Practically every current browser supports it without issue.
- Compress, don't just convert. Even with WebP, it's worth applying compression at around 80-85% quality: the human eye struggles to tell the difference from the original, but the file weighs a fraction of it.
- Resize to the actual display size. If the image is going to be shown at 800 pixels wide on the site, there's no point uploading the original 4,000-pixel file: you're just forcing the browser to download five times more data than it needs.
- Apply lazy loading to images that aren't visible right when the page loads, so the browser doesn't waste time loading photos further down the page until the user actually scrolls there.
The direct link to Core Web Vitals
Google measures your site's real loading experience with a set of metrics called Core Web Vitals, and one of the most important is LCP (Largest Contentful Paint: how long it takes for the largest visible element on screen to appear). On the vast majority of web pages, that largest element is... an image: the header photo, the featured product image, the hero shot. If that image is too heavy, your LCP spikes, and that hits both your ranking and how slow the site feels to whoever's visiting it (which usually translates into people leaving before it even finishes loading).
Put another way: optimising images isn't just about "showing up in Google Images." It's probably the single fastest, cheapest lever for improving your site's overall speed, and speed is, in turn, a direct ranking factor.
Google Images as a traffic source almost nobody looks after
There are entire sectors (recipes, home decor, fashion, DIY, visual tutorials) where a very significant share of traffic comes directly from Google Images, not from regular text search. Someone searches "original wall shelves" in the images tab, sees a photo they like, clicks it, and lands on your site without ever passing through the usual text result. If your images aren't optimised (file name, alt text, correct size, surrounding text context), you simply don't compete in that search, no matter how good the photo is.
A detail people forget: the image sitemap
If you have a lot of important images (a large product catalogue, for example), you can include image information inside your XML sitemap to help Google discover and index them faster, especially if those images load dynamically via JavaScript and might otherwise slip past a normal crawl.
Responsive images: the same photo in several sizes
A technical detail that often gets overlooked: there's no need to serve the same huge image to a 375-pixel-wide phone and to a 1920-pixel desktop monitor. The HTML srcset attribute lets you specify several versions of the same image at different sizes, so the browser automatically picks the most appropriate one based on the device and actual screen size of whoever's viewing it. In practice, this means someone browsing on their phone downloads a much lighter version of the same photo, with no noticeable difference in quality, simply because their screen is smaller and doesn't need any more resolution than that.
Captions matter too
If you add a visible caption under an image (for example, in a blog post with photos of a completed project), that text reinforces the context Google has about the image, in a similar way to alt text, but visible to anyone reading the article. A caption like "Kitchen renovation completed in 15 days" adds concrete information (timeframe, project type) that neither the file name nor the alt text alone usually capture in as much detail, and it also improves the reading experience for anyone just skimming the photos without reading the full text.
Frequently asked questions
What's the maximum an image on my site should weigh?
There's no single figure that applies to everything, but as a practical benchmark: a header or hero image shouldn't exceed 200-300 KB once optimised, and a product image in a catalogue should stay under 100-150 KB. If a single image is over half a megabyte, it can almost always be compressed much further with no visible loss of quality.
Does WebP work in every browser?
Practically yes: every modern browser (Chrome, Firefox, Safari, Edge) has supported it for years. For the rare exception of a very old browser, you can configure an automatic fallback format, but these days it's usually not something worth worrying about.
Is it worth optimising images on a site that's been running for years?
Yes, and it's often one of the best effort-to-result improvements available: you don't need to touch the design or the content, just review and recompress what's already uploaded. On sites with years of photos piled up with no criteria, it's common to cut the page's total weight in half just by optimising the existing images.