Image SEO means making your photos as small, fast and clear as possible, for visitors and for Google. A good photo with a sensible file name, clear alt text and a light file loads quickly and can also be found in Google Images.
On many small business websites, photos are the main reason pages are slow. A photo straight from your phone is often several megabytes, while a few hundred kilobytes is plenty. Below you'll find step by step what to do about it.
Why images matter for SEO
Images affect how easily you're found in two ways. The first is speed. Google measures how quickly the largest element on your page becomes visible, the Largest Contentful Paint (LCP). That element is very often a photo at the top of the page. Google considers an LCP under 2.5 seconds good. A heavy header photo can push you well past that. Read more in our guide to Core Web Vitals.
The second is understanding. Google is getting better at seeing what's in a photo, but it still relies on the text around the image: the file name, the alt text, the caption and the surrounding copy. The clearer these are, the better Google can match your photo to the right search.
Step 1: choose the right file format
Not every format is equally efficient. For most websites, this is a good rule of thumb:
- WebP: small and good quality, works in all modern browsers. A great default for photos.
- AVIF: often even smaller than WebP. Useful if your website supports it.
- JPG: the trusted old format for photos. Fine as a fallback.
- PNG: only for images with transparency or sharp text, such as screenshots. Usually too heavy for photos.
- SVG: for logos and icons. Stays sharp at any size and is usually very small.
Step 2: resize and compress your images
Never upload a photo that is much larger than the size it's shown at on your site. If a photo is displayed at no more than 1200 pixels wide, a 4000-pixel-wide file makes no sense. The browser has to download all of it and then shrink it again.
- Work out the maximum width a photo is shown at and resize it to match.
- Then compress the photo with a tool or plugin. At a quality of around 75 to 85 per cent you usually won't see a difference.
- For ordinary photos, aim for a file of roughly 100 to 300 kilobytes. A large header photo can be a little heavier.
- If possible, let your website create several sizes automatically. That way a phone gets a smaller version than a large screen.
That last point is called responsive images. Your website gives the browser a list of sizes and the browser picks the best one. Modern frameworks and many CMSs do this automatically. On an older site, you may need to have it built in.
Step 3: a sensible file name
IMG_4821.jpg means nothing to anyone. Give your image a short, descriptive name before you upload it. Use lowercase letters and hyphens between words.
- Good: white-washing-machine-repair-at-home.webp
- Less good: washingmachine1.webp
- Don't: washing-machine-repair-cheap-fast-best-washing-machine-engineer.webp
A good file name is a small signal, but it costs you almost nothing and keeps your media library tidier too.
Step 4: write good alt text for your images
Alt text is a short description of the image in the code. A screen reader reads it aloud to people who are visually impaired or blind. Google uses it to understand the photo. And if the photo doesn't load, visitors see the alt text instead of an empty box.
- Describe what is actually in the photo, in a normal sentence.
- Keep it short: one line is usually enough.
- Only use a keyword if it fits what you see.
- Don't start with 'image of' or 'photo of'. A screen reader already announces that it's an image.
- Purely decorative images, such as a line or background pattern, get empty alt text. A screen reader then skips them.
An example for a beauty salon: 'Beautician shaping a client's eyebrows in a bright salon'. That's clear to everyone, and the topic comes up naturally. Good alt text also helps make an accessible website, which deserves extra attention for many businesses since the European Accessibility Act (in force since 28 June 2025).
Step 5: lazy loading and the right order
Lazy loading means the browser only loads an image when the visitor scrolls to it. That makes a big difference on long pages with lots of photos. But note: the photo at the top of the page, which is visible straight away, should NOT be lazy loaded. You want that one shown as quickly as possible, otherwise your LCP gets worse.
- Photos below the fold: lazy loading on.
- Main photo at the top: lazy loading off, and possibly a higher loading priority.
- Give images a fixed width and height in the code. Then the page doesn't jump when photos come in. Google measures that shifting as CLS, which should stay below 0.1.
Common image SEO mistakes
- Uploading photos straight from your phone or camera without resizing them.
- Putting text inside an image instead of on the page. Google and screen readers struggle to read it, and on mobile it often becomes unreadably small.
- Using the same alt text everywhere, or stuffing alt text with keywords.
- A slider with five large photos at the top of the homepage. They all load and slow everything down.
- Stock photos that have nothing to do with your business. They're not forbidden, but your own photos say more. Read tips on using real images in our article on photos on your website.
Images sorted from the build stage
Much of this work can be automated. On the websites we build at Violexa, images are automatically prepared in modern formats and multiple sizes when you upload them, with lazy loading where it belongs. You upload a photo in the CMS and fill in the alt text; the rest happens on its own. This is part of a custom website, from €1,799 excl. VAT (€2,177 incl. VAT), including basic SEO, Google Analytics, CMS integration and training.
Want to know whether your current photos are slowing your site down? Book a free quickscan. In 30 minutes we look at your website together, online or on site. Afterwards you get short written advice with a price estimate, with no obligation.
Frequently asked questions
How do you optimise images for SEO?
Resize the photo to the size it's displayed at, compress it and save it as WebP or AVIF. Give it a descriptive file name and short alt text. Lazy load photos below the fold, but not the main photo at the top.
How large should an image be on a website?
There's no hard limit. For ordinary photos, roughly 100 to 300 kilobytes is a good target. Look mainly at the width: it doesn't need to be larger than the width at which the photo is shown.
What should you write in alt text?
A short, plain sentence describing what's in the image. Include a keyword if it fits, but don't force it. Decorative images get empty alt text.
Is WebP better than JPG?
For most websites, yes. At the same quality, WebP is usually much smaller than JPG and works in all modern browsers. JPG remains a fine fallback.
