Image SEO
Quick Start & Essentials
Image SEO Quick Checklist
The 80/20 of image optimization. Complete these for maximum impact.
Image to WebP Converter
Convert still images to WebP and keep only smaller outputs. Max 100 images at a time.
Drag and drop images here, or click to select
JPG, PNG, BMP supported
Performance & Core Web Vitals
Core Web Vitals Thresholds
Google evaluates the 75th percentile of user experiences. 75% of page visits must meet these thresholds.
| Metric | Good | Needs Improvement | Poor |
|---|---|---|---|
| LCP (Largest Contentful Paint) | 2.5s or less | 2.5-4.0s | >4.0s |
| INP (Interaction to Next Paint) | 200ms or less | 200-500ms | >500ms |
| CLS (Cumulative Layout Shift) | 0.1 or less | 0.1-0.25 | >0.25 |
LCP Image Optimization
Images are the most common LCP element. Prioritize these optimizations.
The fetchpriority attribute tells browsers to load LCP images first.
Google Flights improved LCP from 2.6s to 1.9s (700ms improvement) by adding fetchpriority="high" to their LCP background image.
Critical Lazy Loading Mistake
Lazy loading the LCP image destroys performance.
The loading="lazy" attribute tells browsers to defer downloading until the image is near the viewport. But your LCP image is already in the viewport, creating a delay.
<img src="hero.webp" loading="lazy" />
<img src="hero.webp" fetchpriority="high" />
Preventing Layout Shift (CLS)
Images cause CLS when they load without reserved space. Modern browsers calculate aspect ratio from HTML width and height attributes.
src="image.jpg"
width="800"
height="600"
alt="Description"
/>
The browser calculates aspect ratio (800/600 = 1.33) before the image loads, reserving the correct vertical space.
height: auto;
width: 100%;
}
Target CLS Score: Less than 0.1 for 75% of page visits.
On-Page Image Optimization
Image Format Selection
Google Search supports: BMP, GIF, JPEG, PNG, WebP, SVG, and AVIF.
| Format | Compression vs JPEG | Browser Support | Best For |
|---|---|---|---|
| AVIF | 50% smaller than JPEG | 93%+ | Photos, complex images |
| WebP | 25-34% smaller than JPEG | 97%+ | General use, broad compatibility |
| JPEG | Baseline | Universal | Legacy support |
| PNG | Larger than JPEG | Universal | Transparency, screenshots |
| SVG | Varies | Universal | Logos, icons, illustrations |
AVIF achieves 20-30% smaller file sizes than WebP for lossy compression. However, WebP encoding is faster and has broader browser support. Use <picture> fallbacks for compatibility.
Responsive Images Implementation
Use srcset and sizes attributes to serve optimal images by device.
<source
type="image/avif"
srcset="product-320.avif 320w,
product-640.avif 640w,
product-1200.avif 1200w"
sizes="(max-width: 640px) 100vw, 640px">
<source type="image/webp" ...>
<img
src="product-640.jpg"
alt="Blue leather messenger bag with brass hardware"
width="640" height="480"
loading="lazy" decoding="async">
</picture>
Critical Rule: If you use srcset with w-descriptors, you must include the sizes attribute. Otherwise the browser cannot determine which image to select.
Alt Text Best Practices
Google uses alt text along with computer vision and page context to understand image subject matter.
- Keep alt text concise (80-125 characters recommended for clarity and scannability)
- Describe image content and context
- Don't start with "image of" or "picture of"
- Use empty alt (alt="") for decorative images
- End with a period for screen reader pause
[Product Name] + [Key Feature] + [Variant]
Example: "Blue leather messenger bag with brass hardware."
Common Image SEO Mistakes
Avoid these errors that kill image rankings.
| Mistake | Impact | Fix |
|---|---|---|
| Lazy loading LCP images | Poor LCP scores | Remove loading='lazy' from above-fold images, add fetchpriority='high' |
| Missing width/height attributes | CLS issues | Add dimensions to all images for aspect ratio calculation |
| CSS background-image for content | Images not indexed | Use <img> elements with src attributes |
| Generic filenames (IMG00023.jpg) | Lost context signal | Use descriptive hyphenated names (red-leather-boots.jpg) |
| robots.txt blocking CDN | Images not indexed | Allow Googlebot-Image on CDN domain |
| Missing alt text | Reduced accessibility and context | Add descriptive alt text (80-125 characters) |
File Naming Strategy
Google recommends using hyphens to separate words. Search engines recognize hyphens as word separators while underscores combine words.
Length: Keep filenames under 50-60 characters for readability and URL compatibility.
Target File Sizes
- AVIF: q50-70 (comparable to JPEG q80-90)
- WebP: q75-85 for good balance
- JPEG: q80-85 for web delivery
WordPress Image Optimization Plugins
Comparison of JPEG lossy compression reduction rates from independent testing.
| Plugin | JPEG Reduction | Best For |
|---|---|---|
| ShortPixel | 54% | Overall compression, LCP performance |
| TinyPNG | 45% | Simple bulk optimization |
| EWWW | 44% | Power users, local processing |
| Imagify | 26% | Beginners, simple interface |
| Smush | 17.5% | Ease of use, WordPress beginners |
Technical Infrastructure & Tools
Image Schema Markup
Structured data enables rich results in Google Images, including badges for products, recipes, and videos.
"@context": "https://schema.org",
"@type": "ImageObject",
"contentUrl": "https://example.com/image.jpg",
"license": "https://example.com/license",
"creditText": "Photographer Name",
"copyrightNotice": "2026 Example Company"
}
Required for Rich Results: Product schema with image property (minimum 1200px width recommended for articles).
E-Commerce Platform Requirements
Minimum image specifications for major shopping platforms.
| Platform | Minimum Size | Background | Format |
|---|---|---|---|
| Google Shopping | 100x100px (800x800 recommended) | White preferred | JPEG, PNG |
| Amazon | 1000x1000px | Pure white (RGB 255,255,255) | JPEG, PNG, GIF |
| Shopify | 2048x2048px | Varies | JPEG, PNG |
Front view (primary), back view, side views, detail shots (texture, labels), lifestyle/in-use images, and scale reference. Multiple angles significantly improve Google Lens recognition and visual search matching.
CDN Configuration for SEO
Ensure CDN subdomains allow image crawling.
User-agent: Googlebot
Disallow:
User-agent: Googlebot-image
Disallow:
href="https://cdn.example.com">
<link rel="dns-prefetch"
href="https://cdn.example.com">
Image Sitemap
Reference XML format for declaring images to Google.
Google Search Console Image Reports
Access image-specific performance data in GSC.
- Navigate to Performance then Search Results
- Click Search Type filter
- Select Image instead of Web
How Google Processes Images
Understanding Google's image crawling and indexing pipeline.
Images found through HTML parsing of src attributes in img elements, image sitemaps, and linked pages. CSS background images are NOT indexed.
OCR extracts text, computer vision analyzes content alongside alt text and page context, quality scoring evaluates sharpness and resolution.
Google identifies duplicate images across domains using canonical signals and timestamps to determine the original source.
Critical: Use standard HTML img elements with src attributes. CSS background-image is NOT indexed by Googlebot-Image.
Image Ranking Factors
Confirmed signals Google uses to rank images in search results.
| Factor | Type | Description |
|---|---|---|
| Alt text + surrounding content | On-page | Primary context signals for image relevance |
| Page authority | Off-page | Higher-authority pages rank images better |
| Image quality | Technical | Sharp, high-resolution images preferred |
| Engagement signals | Behavioral | Click-through rates from image results |
| Structured data | Technical | Enables rich results and badges |
| File name | On-page | Light signal for subject matter |
Context Signals Beyond Alt Text
Google extracts image context from multiple page sources.
Place images near relevant content for topical association.
The H2/H3 above an image affects its topical association.
Provide additional context that Google uses for ranking.
Create unique landing pages for important images rather than grouping them in galleries. Standalone pages allow for richer metadata and descriptive text that help Google associate images with specific queries.
INP Optimization for Images
Large images in the DOM can affect Interaction to Next Paint through layout recalculation.
Good INP Score: Under 200 milliseconds for 75% of page visits.
Image CDN Comparison
All major image CDNs support automatic WebP/AVIF conversion, caching, and signed URLs.
| Service | Key Features | Pricing Model |
|---|---|---|
| Cloudinary | Multi-CDN, auto-format, comprehensive transformations | Credit-based |
| ImageKit | Transparent pricing, free tier 20GB, auto-format | Bandwidth-based |
| Imgix | Granular URL transforms, developer-focused | Request/bandwidth |
| Bunny Optimizer | Budget-friendly, simple integration | Flat fee |
AI-Generated Images and C2PA
Google has adopted the C2PA (Coalition for Content Provenance and Authenticity) standard.
- C2PA metadata embedded in image files indicates how the image was created
- Google extracts this metadata and may display it in "About this image" feature
- Tools like Adobe Firefly or Midjourney may embed C2PA metadata automatically
Note: No current evidence of ranking penalties for AI-generated images, but transparency through metadata is recommended for long-term trust.
Implementation Code Examples
Copy-ready snippets for prioritizing, framing, and structuring images.
Compression Tools
| Tool | Type | Best For |
|---|---|---|
| ShortPixel | WordPress plugin + API | Best overall compression |
| Squoosh | Web app (free) | Manual optimization |
| sharp | Node.js library | Build pipelines |
| Cloudinary | CDN + API | Auto-optimization at scale |
Audit Tools
| Tool | Use Case | Pricing |
|---|---|---|
| Screaming Frog | Comprehensive crawls | Free (500 URLs) / £199/yr (~$279/yr) |
| PageSpeed Insights | Core Web Vitals | Free |
| GSC Image Report | Traffic analysis | Free |
| Sitebulb | Visual audits | £13.50+/mo |
Screaming Frog Image Audit Settings
Recommended configuration for comprehensive image audits.
- Enable "Extract images from img srcset Attribute"
- Store HTML and Rendered HTML for JS-heavy sites
- Add CDN domains (e.g., cdn.example.com) as internal
- Ensures images on CDNs are audited
- Set to "Googlebot (Smartphone)"
- See mobile experience as Google does
Ongoing Optimization
Maintain image SEO performance with these regular tasks.