Image SEO gets treated as an afterthought, and it is usually the largest single thing slowing a site down. Pictures are heavy, they load before the words, and most sites publish them straight from a camera or a stock library.
This article covers what to do with them.
Image SEO starts with file size
A photograph exported at full resolution can be several megabytes, and a page waits for it. Meanwhile the visitor is on a phone with an ordinary connection, watching a blank space.
Two steps solve most of it. Resize the image to the largest size it will actually be displayed at, because sending a huge picture to be shown small wastes everything it costs. Then compress it, which removes detail nobody can see at that size.
Doing both to your busiest templates usually improves a site more than any other single change, and it needs no developer on most platforms. Set against what else decides where a page ranks, pictures are only one part of the job.
Alt text is for readers first
Alternative text describes a picture to somebody who cannot see it. That is its purpose, and search engines read it as a useful side effect.
Write what the image actually shows, plainly, as if describing it aloud. "Engineer replacing a boiler valve in a kitchen" is useful. "boiler repair boiler service boiler engineer" is stuffing, and it fails the person who needed the description.
Decorative images need empty alt text rather than a description, so a screen reader skips them. Image SEO advice often misses that, and describing a background swirl helps nobody.
Image SEO details worth two minutes each
A file called IMG_4821.jpg says nothing. Renaming it to something descriptive before upload is a small, free improvement and it takes seconds.
Beyond that, declare width and height on every image so the browser leaves room for it, which stops the page jumping while it loads. Use lazy loading for pictures below the fold and eager loading for the one at the top, since delaying the main image is the one place lazy loading hurts.
Which format to use
Modern formats are considerably smaller than the older ones at the same visible quality, and every current browser supports them. Most platforms convert automatically now, so this is often a setting rather than a task.
For anything with flat colour and sharp edges, such as a logo or a diagram, a vector file stays crisp at every size and is usually tiny. Photographs need a photographic format. Using the wrong one either bloats the file or blurs the edges.
Image SEO for search results
Pictures appear in their own search results and inside ordinary ones, which is worth a little effort where the image is genuinely the point.
Three things help. Put the image near text that explains it, since the surrounding words are how a search engine works out what it shows. Use a descriptive file name and alt text. Include images in your sitemap if your platform offers it.
Set expectations though. Image search sends meaningful traffic to recipe sites, retailers and anything visual, and very little to most service businesses.
How many images a page needs
Fewer than most people think. An image earns its place by explaining something the words cannot, or by showing the thing being described. A picture that merely breaks up text costs loading time and returns nothing.
Screenshots, diagrams and photographs of real work all pass that test easily. Generic stock photography rarely does, and readers have learned to skip it entirely.
So the honest count is one per idea that genuinely needs showing, and none at all where the writing is clear on its own.
The mistakes worth avoiding
- Uploading straight from a camera, which is the single most common cause of a slow page.
- Text inside an image, which no search engine reads reliably and no screen reader reads at all.
- Repeating a keyword in every alt attribute, which helps nothing and hurts accessibility.
- Lazy loading the main image at the top of the page, which delays the thing you most want to appear.
- Stock photographs of handshakes, which cost loading time and persuade nobody.
Image SEO on a site that already has hundreds
Fixing every picture on an established site is not realistic, and it is not necessary either. Traffic concentrates, so the work should too.
Take the twenty pages that get the most visits and fix only those. Resize, compress, rename and describe. That is an afternoon, and it covers the pages where a slow load actually costs you something.
For everything else, change the settings so new uploads are handled properly and let the old pages be. A backlog nobody visits is not a problem worth an afternoon.
A ten minute image SEO routine
Before publishing anything, do four things. Resize the picture to the width it will display at. Compress it. Rename the file to describe it. Write alt text you would be happy reading aloud to somebody on the phone.
That is the whole discipline for most sites. Everything else is refinement, and none of it matters while the page is still loading a four megabyte photograph.
Frequently asked questions
What is image SEO?
It is the work of making pictures help a page rather than slow it down: sizing and compressing them so the page loads quickly, describing them properly for readers and search engines, and naming files usefully. Speed is the part that matters most.
What alt text should I write?
Describe what the picture actually shows, plainly, as if saying it aloud to somebody who cannot see it. That serves screen reader users, which is its purpose, and search engines read it as a side effect. Repeating a keyword instead fails both.
Do decorative images need alt text?
They need empty alt text rather than a description, so a screen reader skips them. Describing a background pattern or a divider helps nobody and adds noise. Only images carrying meaning need describing.
How much should I compress images?
Enough that the file is small and the picture still looks right at the size it appears. Resize first, because sending a huge image to be displayed small wastes everything it costs, then compress to remove detail nobody can see at that size.
Which image format is best?
A modern photographic format for photographs, since they are considerably smaller at the same visible quality and every current browser supports them. A vector file for logos and diagrams, because it stays crisp at any size and is usually tiny.
Does image search bring real traffic?
It depends entirely on the business. Recipe sites, retailers and anything visual can get meaningful traffic. Most service businesses get very little, so image SEO for them is about page speed and accessibility rather than about appearing in image results.
Should I put text inside images?
No. No search engine reads it reliably and no screen reader reads it at all, so the words effectively do not exist. If the text matters, it belongs on the page as text, with the image alongside it rather than containing it.
What is the most common image mistake?
Uploading straight from a camera or a stock library without resizing. A single photograph can be several megabytes and the page waits for it. Fixing that on your busiest templates usually improves a site more than any other single change.