Image SEO: How to Optimise Images for Google Search
Images help readers understand a page, and they can bring visitors from image search. Google needs to find, understand and load them. This guide covers alt text, file names, formats, speed and placement, with a step-by-step method for WordPress.
- Alt text examples
- Supported formats
- Speed tips
- Based on Google’s docs
| Check | Good example |
|---|---|
| File name | red-running-shoes.webp |
| Alt text | Red running shoes on a wooden floor |
| Format | WebP, AVIF, JPEG or PNG |
| Size | Compressed, not oversized |
| Placement | Next to the text it illustrates |
What image SEO is and why it matters
Image SEO means making your images easy for Google to find and understand, and quick for visitors to load. It has three jobs: help your page rank for its topic, make your site accessible to people who use screen readers, and make your images eligible to appear in Google Images.
Google says it uses the content around an image, including captions and image titles, to understand what the image is about. It also says images are often the biggest part of page weight, so optimising them helps speed.
Image SEO is rarely the main reason a page ranks. It supports the page, so do it alongside your on-page SEO checklist.
- Use real image elements Google can index
- Describe the image in alt text
- Name files with short words
- Keep files light
- Place images near related text
How Google finds your images
Use a real image element
Google indexes standard <img> tags with a src attribute. It does not index CSS background images.
Responsive images need a fallback
If you use srcset or <picture>, always include an <img> with a src fallback.
How to write alt text
Google calls alt text the most important image metadata. It describes the image for people who cannot see it and gives Google context.
| Image | Weak alt text | Better alt text |
|---|---|---|
| Product photo | shoes | Red running shoes, side view |
| Chart | chart | Line chart showing organic visits rising over six months |
| Stuffed | cheap shoes buy shoes best shoes online | Pair of red running shoes on a wooden floor |
| Decorative | decorative swirl image | Empty alt text (alt=””) so screen readers skip it |
Rules: describe what is in the image, keep it useful and in context, and do not stuff keywords. If an image is also a link, the alt text works as the link’s anchor text. Empty alt for purely decorative images is an accessibility convention rather than a Google ranking rule.
File names, formats and speed
Short and descriptive
Use red-running-shoes.webp rather than IMG_4021.jpg. Google recommends short, descriptive names.
Supported types
Google supports BMP, GIF, JPEG, PNG, WebP, SVG and AVIF. Keep the file extension matching the real file type.
Keep files light
Compress images and test with PageSpeed Insights. Large images slow pages. See Core Web Vitals for WordPress.
Which format to pick for each image is a practical choice. As a general rule of thumb, photos suit JPEG, WebP or AVIF, simple graphics suit PNG, WebP or SVG. This is not a Google rule.
How to optimise an image before and after upload
Pick a relevant image
Choose a sharp image that adds meaning to the page. Google says sharp, high-quality images appeal more to users and look better in search thumbnails.
Resize and compress
Resize to the largest size your layout needs, then compress. Uploading a very large photo and letting the browser shrink it wastes bandwidth.
Rename the file
Use lowercase words separated by hyphens, such as red-running-shoes.webp.
Upload to the Media Library
Go to Media, Add New. After upload, click the image to open its details.
Fill in Alt Text and Caption
Write alt text that describes the image. Add a caption when it helps readers, because Google uses captions as context.
Place it near related text
Put the image close to the paragraph it supports, on a page about that topic.
Check it loads
View the page on mobile, run PageSpeed Insights, and use URL Inspection in Search Console to see the rendered page. See the Search Console setup guide.
Other things Google mentions
Image sitemaps
Help Google find images it might miss. You can list images hosted on another domain, such as a CDN, and Google suggests verifying that domain in Search Console. See robots.txt and sitemaps.
Preferred image for a page
You can signal the main image with og:image or structured data. Avoid logos, images dominated by text, and extreme aspect ratios.
Same URL everywhere
Use the same image URL when you reuse an image across pages, so Google can cache it.
Data URIs
Google says images can be embedded as data URIs, but they can noticeably increase page size, so use them sparingly.
Mistakes to avoid
Text baked into images
Google cannot rely on text in a picture the way it reads page text.
CSS background images for content
Google does not index them.
Missing or stuffed alt text
Both lose the benefit.
Huge unoptimised files
They slow the page.
Generic file names
Names like image1.jpg add no context.
Image SEO questions
Is alt text a ranking factor?
Google calls it the most important image metadata attribute and uses it to understand images. Google does not state a precise ranking weight, so write it for users first.
How long should alt text be?
Google gives no length. Keep it as short as it can be while still describing the image usefully.
Which image format is best for SEO?
Google supports several formats and does not name one as best. Choose the format that keeps quality good at a small file size.
Do I need alt text on every image?
Add descriptive alt text to every meaningful image. Purely decorative images can have empty alt text.
Do image file names matter?
Google recommends short, descriptive names over generic ones, so it is an easy habit to adopt.
Format choice by image type and decorative-image alt text are general practice, not Google rules. Examples use fictional files.