How to Optimise Images for SEO in 2026

Images affect SEO in more ways than most people realise. Poor image optimisation is one of the top reasons pages fail Core Web Vitals and lose rankings. Here is a complete image SEO checklist for 2026.

1. File Size: The Most Impactful Factor

• Oversized images are the single biggest cause of slow page speeds. Google's PageSpeed Insights routinely identifies 'properly size images' and 'serve images in next-gen formats' as top recommendations. The targets:
• Hero images: Under 150–200KB
• Blog thumbnails: Under 80–100KB
• Product images: Under 100–150KB
• Use Image Compressor to reduce file sizes, or hit exact targets with Compress to 100KB.

2. Format: Switch to WebP

Google explicitly recommends serving images in WebP format as part of its PageSpeed guidance. Converting JPG images to WebP reduces file size by 25–35% with no visible quality loss. Convert JPG to WebP — the impact on your LCP score is immediate and measurable.

3. Descriptive File Names

• Search engines read file names as signals about image content.
• Bad: `IMG_4823.jpg`
• Good: `how-to-resize-image-for-instagram.webp`
• Use hyphens, not underscores. Keep it under 5 words. Include your target keyword naturally.

4. Alt Text: Descriptive, Not Keyword-Stuffed

• Alt text tells search engines what an image shows. Guidelines:
• Describe the image accurately in 5–15 words
• Include the target keyword if it naturally fits
• Do not write "image of" or "photo of"
• Leave decorative images with empty alt=""
• Example: `alt="man compressing photo on laptop using free online tool"`

5. Dimensions: Serve at Display Size

Sending a 2000px image to fill a 600px container wastes bandwidth and slows LCP. Always resize images to their actual display size. Use Image Resizer to set exact dimensions before upload.

6. Structured Data for Image SEO

For recipes, products, and articles, add `ImageObject` structured data to your schema. Google uses this for rich results that include images in SERPs. Articles with `image` properties in Article schema are eligible for Google Image SERP features.

7. Image Sitemaps

Include image URLs in your sitemap using the `<image:image>` extension. This helps Google discover and index images it might otherwise miss, particularly JavaScript-rendered images.

8. Lazy Loading

Add `loading="lazy"` to all images below the fold. This defers loading until the user scrolls near them, improving initial page load time and LCP for the above-fold content.

Core Web Vitals: The Image Targets

• LCP (Largest Contentful Paint): Under 2.5 seconds. Usually triggered by the hero image. Compress to under 150KB and serve as WebP.
• CLS (Cumulative Layout Shift): Under 0.1. Always include `width` and `height` attributes on `<img>` tags so the browser reserves space before the image loads.
• FCP (First Contentful Paint): Preload your hero image with `<link rel="preload">`.