Image SEO: alt text, file names and what actually matters

Image SEO is simpler than most guides make it sound. Google's own documentation boils down to a few clear practices. Here's what actually moves the needle.

The three things that matter

Alt text: A short description of what the image shows
File name: A descriptive, hyphenated file name
Page context: The surrounding text and heading structure

Everything else — EXIF data, image sitemaps, structured data for images — is secondary. Get these three right and you've covered 90% of image SEO.

Writing good alt text

Alt text serves two purposes: accessibility (screen readers) and SEO (search engines). Write for the person who can't see the image.

Good alt text:

<img alt="Golden retriever playing fetch on a sandy beach" />

Bad alt text:

<img alt="image" />
<img alt="dog photo stock image beach dog golden retriever puppy" />
<img alt="" />
<!-- empty when the image conveys meaning -->

Guidelines:

Describe what the image shows, not what it is ("a woman coding" not "stock photo")
Keep it under 125 characters (screen readers may truncate longer text)
Don't stuff keywords — write naturally
Use empty alt (alt="") only for purely decorative images

File naming

Search engines use file names as a signal for image content. Compare:

❌ IMG_20260301_142355.jpg
❌ photo-1.jpg
✅ golden-retriever-beach-fetch.jpg

Use lowercase letters, hyphens (not underscores), and descriptive words. The file name should make sense to someone who can't see the image.

Image sitemaps (optional)

If your images are important for discovery (product photos, infographics, original photography), you can include them in your sitemap:

<url>
  <loc>https://example.com/products/widget</loc>
  <image:image>
    <image:loc>https://example.com/images/widget-blue.jpg</image:loc>
  </image:image>
</url>

For most sites, this is unnecessary — Google discovers images by crawling your pages.

Technical optimisation for SEO

Beyond content, there are technical factors that affect image SEO:

Page speed

Google uses Core Web Vitals as a ranking factor. Heavy images slow your page down, which hurts rankings. Compress your images and serve them in modern formats.

Responsive images

Use srcset to serve different sizes for different screens. This improves page speed on mobile — where most searches happen.

Lazy loading

Use loading="lazy" on below-fold images. This improves initial page load without affecting crawlability — Google renders JavaScript and sees lazy-loaded images.

Structured data

For product images, recipe images, and how-to images, structured data (Schema.org) can trigger rich results in Google Search. But for general blog images, this isn't necessary.

The checklist

For every image on your site:

[ ] Descriptive file name (kebab-case, no random strings)
[ ] Meaningful alt text (under 125 characters)
[ ] Width and height attributes set
[ ] Compressed to a reasonable file size
[ ] Served in WebP or AVIF format
[ ] Below-fold images lazy loaded

That's it. No tricks, no hacks, no keyword stuffing. Just make your images descriptive, fast, and accessible.