By The Creaiter team · · 8 min read
Image SEO: Alt Text, File Size and Getting Found in Image Search
Image SEO sounds like a niche concern and is actually three practical wins stacked on top of each other. Images are usually the largest files on a page, so fixing them is the fastest route to a faster site. Alt text is what a screen reader announces, so getting it right is an accessibility obligation before it is a ranking one. And image search is a genuine traffic source for anything visual that almost nobody competes for properly.
None of it is difficult. Most of it is a habit applied at upload time, which is the only time it costs nothing.
Alt text that does a job
Alt text describes the image to someone who cannot see it. That is the whole specification, and almost every mistake comes from forgetting it and treating the field as a place to put keywords.
The test is simple. Read your alt text aloud with your eyes closed. If it tells you what the picture shows, it is right. If it reads like a search query, it is wrong, and it is wrong in a way that makes the page worse for a blind visitor in order to chase a signal that stopped working years ago.
One nuance worth knowing: a purely decorative image should have an empty alt attribute rather than a description. That tells a screen reader to skip it, which is the correct behaviour for a background flourish. Omitting the attribute entirely is different and worse, because some readers will then announce the file name.
- alt="marketing software best marketing tool AI marketing"
- alt="IMG_4471.jpg"
- alt="image"
- Same alt text repeated on every image in the post
- alt="Content calendar showing four posts scheduled across one week"
- alt="Bar chart comparing organic and paid traffic over six months"
- alt="" on a decorative background pattern, so readers skip it
- A different description for each image, because they show different things
File names, formats and size
Rename the file before you upload it. A camera gives you DSC_0912.jpg, which tells a search engine nothing. Something like blue-ceramic-mug-on-desk.jpg is a free, permanent description that travels with the file wherever it ends up.
Format matters more than most people expect. Modern formats produce a visually identical picture at a fraction of the size of an older JPEG or PNG, and support is now effectively universal. Keep PNG for things that genuinely need transparency or hard edges like logos and screenshots of text. Use vector formats for logos and icons, which stay sharp at any size and are usually tiny.
Then size them correctly, which is the single most common miss. An image displayed at eight hundred pixels wide should not be a three thousand pixel file. The browser will scale it down and it will look fine, which is exactly why nobody notices they are shipping several megabytes to a phone.
- Rename files descriptively, with hyphens, before uploading
- Use a modern format for photographs, PNG only where you need transparency
- Export at roughly twice the display width for sharp screens, no more
- Compress after exporting, since most exports leave room
- Lazy-load everything below the fold, and never the hero image
Getting into image search
Image search is a separate results page with its own traffic, and it favours the sites that make images easy to understand. That means the alt text and file name above, plus context: an image surrounded by relevant text is easier to classify than one floating alone.
A caption helps more than people expect, because it is visible text explicitly tied to the picture. Not every image needs one, but a chart or a screenshot almost always benefits from a line saying what to look at.
If images are a meaningful part of your business, add an image sitemap or include image entries in your existing one. It is the difference between hoping a crawler finds your gallery and telling it where the gallery is.
The one that costs you traffic silently
Hosting images on a different domain from your content is common with a content delivery network and usually fine, but check that the images are actually attributed to your site rather than the delivery domain. Otherwise your image search traffic accrues to a hostname nobody can visit.
The other quiet loss is stock photography. A stock image is on thousands of sites, so it will never rank in image search and it makes your page look like every other page on the topic. An ordinary photograph you took yourself outperforms a polished stock image on both counts.
Common questions
- What makes good alt text?
- A short description of what the image shows, written for someone who cannot see it. Read it aloud with your eyes closed and ask whether you now know what the picture contains. Keywords belong in it only when they genuinely describe the image. A decorative image should have an empty alt attribute so screen readers skip it rather than announcing a file name.
- What size should images be for a website?
- Export at roughly twice the width the image is displayed at, which keeps it sharp on high-resolution screens without being wasteful, then compress. The frequent mistake is uploading straight from a camera or a design tool at several thousand pixels wide. The browser scales it down so it looks correct, which is why the problem goes unnoticed while costing seconds on a phone.
- Which image format should I use?
- A modern format such as WebP or AVIF for photographs, since they produce a visually identical picture at a fraction of the file size and support is now effectively universal. Keep PNG for images needing genuine transparency or crisp text edges like logos and screenshots. Use SVG for logos and icons, which stay sharp at any size and are usually very small.
- Do images help SEO?
- In three ways. They are usually the heaviest thing on a page, so optimising them is the fastest speed win available. Alt text makes the page usable for screen reader visitors, which is an obligation in its own right. And image search is a separate traffic source that most sites never compete for properly, so it is unusually winnable for anything visual.
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