Learning how to optimise images for SEO is one of the fastest wins a small business can pull off in 2026. Images make up roughly 41% of the average webpage weight, more than any other resource type (HTTP Archive Web Almanac, 2024). Fix the images and you fix half your speed problem.
This guide walks through the exact process we use at The 66th when auditing client sites. No fluff, no theory, just the steps that move rankings and Core Web Vitals scores.
Why Do Images Matter So Much for SEO in 2026?
Google confirmed that page experience signals, including Largest Contentful Paint (LCP), are ranking factors in every core update since 2021 (Google Search Central, 2024). LCP is almost always an image. If your hero image takes 4 seconds to load, that is your LCP score, and it drags your rankings with it.
Beyond speed, images are a traffic channel of their own. Google Images drives around 22.6% of all search queries globally (Semrush, 2024). Most SMBs ignore this entirely.
The 3 signals Google reads from an image
Google looks at the file itself, the surrounding HTML, and the page context. Filename, alt text, caption, nearby text, and structured data all feed the picture.
Miss any of these and you leave ranking signals on the table. Get them right and you show up in both regular search and image search.
What changed for images in 2026
AI Overviews now pull thumbnail images directly into answer panels. Pages with clean, well-labelled images get pulled in far more often than pages with generic stock photos. If you want to appear in AI Overviews, your images have to earn their place.
Which Image Format Should You Actually Use?
Format choice sets your ceiling. Pick wrong and no amount of compression saves you.
WebP is the default for photos and complex graphics in 2026. It cuts file size by 25 to 35% compared to JPEG at the same quality (Google Developers, 2024). AVIF cuts even more, around 50%, but browser support is still catching up.
Format comparison at a glance
| Format | Best for | Avg size vs JPEG | Browser support |
|---|---|---|---|
| WebP | Photos, product shots, hero images | ~70% | 97%+ |
| AVIF | Large photos where speed matters most | ~50% | 93%+ |
| SVG | Logos, icons, simple illustrations | Often under 5KB | 100% |
| PNG | Screenshots, images needing transparency | 110-130% | 100% |
| JPEG | Fallback only | 100% | 100% |
When to keep the old format
Screenshots of interfaces stay as PNG. Logos stay as SVG. Everything else, photos, product images, blog headers, converts to WebP or AVIF.
How Big Should Your Images Be Before You Upload Them?
Uploading a 4000-pixel-wide photo to display in a 800-pixel container is the single most common mistake we see on SMB sites. The browser downloads all 4000 pixels, then squishes them. Speed suffers, ranking suffers.
The 2x rule for dimensions
Figure out the largest display size across your breakpoints. Multiply by 2 for retina screens. That is your maximum upload width.
A hero image that displays at 1200px wide should be exported at 2400px, not 6000px. A blog thumbnail shown at 400px should be 800px, not 3000px.
Target file sizes for 2026
Hero images: under 200KB. Content images: under 100KB. Thumbnails: under 40KB. If you cannot hit these targets while keeping the image sharp, your dimensions are too big or you are using the wrong format.
What Does Proper Image HTML Look Like?
Compressing the file is half the job. The HTML has to be right too, or you will still fail Core Web Vitals.
The 4 attributes every image tag needs
Width and height attributes prevent layout shift. Loading equals lazy defers offscreen images. Alt text describes the image for search engines and screen readers. Srcset serves the right size to each device.
Skip any of these and you leave performance on the table. Skip alt text and you also lose the image search opportunity.
Alt text that actually helps you rank
Bad alt text: "image1.jpg" or "picture of dog". Good alt text: "golden retriever puppy sitting on hardwood floor beside chew toy". Descriptive, specific, and includes natural keyword phrasing when it fits the image.
Do not stuff keywords. Google flagged keyword-stuffed alt text as a spam signal in the March 2024 core update and every update since (Google Search Central, 2024). Describe what is actually in the image.
Filenames matter more than people think
DSC_04728.jpg tells Google nothing. vancouver-dental-clinic-reception.jpg tells Google everything. Rename before upload, using hyphens and lowercase.
How Do You Actually Measure If Any of This Is Working?
You cannot improve what you do not measure. Two tools do 90% of the work.
PageSpeed Insights for the technical view
Run your top 5 pages through PageSpeed Insights monthly. Look at LCP, and specifically which element is the LCP. If it is an image, that image is where you focus.
Aim for LCP under 2.5 seconds on mobile. Sites hitting this threshold see 24% higher conversion rates than sites over 4 seconds (web.dev, 2024).
Search Console for the ranking view
The Performance report in Search Console has a Search Appearance filter. Switch it to "Image" and you see every query bringing image traffic. Most SMBs have never opened this view.
If you want help interpreting these reports, our tracking guide covers what actually matters.
The monthly image audit checklist
Every 30 days, scan new images uploaded that month. Check file size, format, alt text, and filename. Fix anything that slipped through. This 20-minute habit prevents the slow bloat that kills most SMB sites over 2 years.
What Order Should You Actually Fix This Stuff In?
Prioritise by traffic. Homepage first, then top 5 landing pages, then blog. Do not try to fix 400 images in one weekend.
Week 1: The hero images
Every page has one big image above the fold. Convert to WebP, resize to 2x display dimensions, compress to under 200KB, add proper alt text. Done.
This one week of work moved WashTech's LCP from 4.1 seconds to 1.8 seconds. Rankings followed within 6 weeks.
Week 2: The service and product pages
These pages drive revenue. Every image on them earns its place or gets deleted. If an image does not help the buying decision, cut it.
Week 3 onwards: The blog
Blog images matter less than commercial page images. Batch them. Convert 20 to 30 per session using a tool like Squoosh or ImageOptim.
Key Takeaways
- Images are 41% of page weight and usually the LCP element that Google ranks on.
- WebP is the default format for photos in 2026. AVIF where you can, SVG for logos, PNG only for screenshots.
- Resize before upload to 2x display dimensions, not 6x.
- Every image needs width, height, loading, alt, and srcset attributes.
- Descriptive filenames and alt text win image search traffic that most competitors ignore.
- Measure LCP monthly in PageSpeed Insights and image traffic in Search Console.
- Fix in order of traffic value: homepage, commercial pages, blog.
Frequently Asked Questions
What is the best image size for SEO in 2026?
The best image size is 2x the largest display dimension, saved as WebP, and compressed to under 200KB for hero images or under 100KB for content images. A hero displayed at 1200px wide should be exported at 2400px and kept under 200KB.
Does alt text still matter for SEO?
Yes. Alt text helps Google understand image content, drives image search traffic, and supports accessibility. Write descriptive alt text that explains what is in the image, using natural language and relevant keywords only when they fit.
Should I use WebP or AVIF for my website?
Use WebP as your default in 2026. It has 97% browser support and cuts file size by 25 to 35% versus JPEG. Use AVIF for large photos where speed is critical and your CMS supports fallbacks, since it saves another 20 to 30%.
How do I compress images without losing quality?
Use tools like Squoosh, ImageOptim, or ShortPixel. Start at 80% quality for JPEG or WebP. Compare the compressed version side by side with the original. Most photos look identical at 75 to 85% quality but weigh half as much.
Do image filenames affect SEO?
Yes. Google reads filenames as a ranking signal for image search. Rename files with descriptive, hyphenated, lowercase names before uploading. "vancouver-dental-clinic-reception.jpg" beats "IMG_2847.jpg" every time.
How many images should a blog post have?
Enough to support the content, no more. 1 hero image plus 2 to 4 supporting visuals for a 1500-word post is typical. Extra images that do not add information slow the page and dilute the signal.
Can lazy loading hurt my SEO?
Only if you lazy load your LCP image. The image above the fold should load immediately. Lazy load everything below the fold using loading="lazy". This is the current Google recommendation and works in all modern browsers.
If you want help auditing your images and the rest of your on-page setup, our team at The 66th runs technical SEO audits for local businesses across Canada. Start with our free audit tool or get in touch.
