image-seo-audit（图像 SEO 审核）

/dm:image-seo-audit

Purpose

Perform a dedicated image optimization audit that evaluates all images on a page or site for SEO, performance, and accessibility. Produces a prioritized optimization list sorted by file size impact.

Input Required

• URL: Page or site to audit
• Scope: Single page or site-wide crawl (default: single page)

Process

1. Load brand context: Read active brand profile for industry context.
2. Discover images: Find all <img>, <picture>, CSS background-image, and <source> elements.
3. Alt text audit: Check presence, quality, keyword inclusion, length (10-125 chars). Flag: missing, filename-only ("image.jpg"), keyword-stuffed, non-descriptive ("click here").
4. File size audit: Apply tiered thresholds by image category — thumbnails (<50KB target, >200KB critical), content images (<100KB target, >500KB critical), hero/banner (<200KB target, >700KB critical).
5. Format audit: Check for modern formats. Recommend WebP (97%+ support) or AVIF (92%+ support) over JPEG/PNG. Check for <picture> element with format fallbacks. Note: JPEG XL restored in Chromium (Nov 2025) but not yet in Chrome stable — monitor, don't recommend yet.
6. Responsive images: Check for srcset and sizes attributes, appropriate resolution for device pixel ratios.
7. Lazy loading: Verify loading="lazy" on below-fold images. Flag loading="lazy" on above-fold/hero images (directly harms LCP).
8. fetchpriority: Check for fetchpriority="high" on LCP/hero images. Check for decoding="async" on non-LCP images.
9. CLS prevention: Check for width and height attributes or aspect-ratio CSS on all <img> elements. Flag images without dimensions.
10. File naming: Check for descriptive, hyphenated, lowercase file names vs generic names (IMG_1234.jpg).
11. CDN usage: Check if images are served from a CDN (different domain, CDN headers, edge caching).
12. Score and prioritize: Sort by file size savings impact (largest first).

Recommended Picture Element Pattern

<picture>
  <source srcset="image.avif" type="image/avif">
  <source srcset="image.webp" type="image/webp">
  <img src="image.jpg" alt="Descriptive alt text" width="800" height="600" loading="lazy" decoding="async">
</picture>

Hero/LCP Image Pattern

<img src="hero.webp" fetchpriority="high" alt="Hero image description" width="1200" height="630">

Do NOT lazy-load above-fold/LCP images. Do NOT add decoding="async" to LCP images.

Output

Image Audit Summary

Prioritized Optimization List

Sorted by estimated file size savings (largest first):

Recommendations (prioritized)

1. Convert X images to WebP format (est. XX KB total savings)
2. Add alt text to X images
3. Add width/height dimensions to X images
4. Enable lazy loading on X below-fold images
5. Add fetchpriority="high" to LCP image
6. Compress X oversized images
7. Implement <picture> element with AVIF/WebP fallbacks

Agents Used

• seo-specialist — Image optimization analysis, CWV impact assessment

Scripts Used

• tech-seo-auditor.py — Fetch page and analyze image elements