Image Optimization Analysis

使用范围与安全规则

本 Skill 只用于“网站图片替代文本审计”场景，围绕用户当前提供或明确授权处理的材料完成任务。功能目标：检查图片替代文本是否缺失、空泛、堆词或长度不当，并生成兼顾无障碍与搜索语义的修改建议。

• 默认先在回复中交付分析、方案、草稿、代码建议或检查清单，不主动读取任务范围外的文件、账号和数据。
• 信息不足时先标记缺口并向用户确认，不用猜测内容填补事实、数字、姓名、结论或权限。
• 需要联网检索或调用接口时，先说明访问目标、拟发送的数据和用途并取得用户明确同意；只访问用户指定或公开合法来源，不绕过登录、付费墙、验证码、访问控制或平台限制。
• 涉及发送、发布、上传、删除、支付、投放、部署、同步或其他外部写入时，先展示目标、内容和影响，获得用户对该次动作的明确确认后再执行。
• 不要求用户在对话里粘贴密码、Cookie、Token、API Key 或私钥；凭据仅用于用户指定的对应官方服务，不回显、不记录、不写入交付物，也不转发到无关地址。
• 命令和脚本默认作为可审查的参考方案；只有用户明确要求执行、目标路径与影响范围清楚且完成预检后，才运行必要的最小步骤。
• 营销与增长输出只做合规方案、内容草稿和测试建议，不承诺流量、排名、成交或收益；不刷量、不群发骚扰、不伪造背书，不设计规避平台规则的做法。
• 交付前复核事实依据、隐私、版权、平台规则和可执行边界；发现高风险或越权请求时停止相关动作，并给出合规替代方案。

Checks

Alt Text

• Present on all <img> elements (except decorative: role="presentation")
• Descriptive: describes the image content, not "image.jpg" or "photo"
• Includes relevant keywords where natural, not keyword-stuffed
• Length: 10-125 characters

Good examples:
- "Professional plumber repairing kitchen sink faucet"
- "Red 2024 Toyota Camry sedan front view"
- "Team meeting in modern office conference room"

Bad examples:
- "image.jpg" (filename, not description)
- "plumber plumbing plumber services" (keyword stuffing)
- "Click here" (not descriptive)

File Size

Tiered thresholds by image category:

Recommend compression to target thresholds where possible without quality loss.

Format

Recommend WebP/AVIF over JPEG/PNG. Check for <picture> element with format fallbacks.

Recommended <picture> Element Pattern

Use progressive enhancement with the most efficient format first:

<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>

The browser will use the first supported format. Current browser support: AVIF 93.8%, WebP 95.3%.

JPEG XL: Emerging Format

Third-party reporting and Wikipedia describe a Rust-based JPEG XL decoder as shipped in Chrome 145 stable (2026-02-10) behind the chrome://flags/#enable-jxl-image-format flag, not enabled by default; no Google-owned confirmation was retrieved in the fact pack. Because default support is not confirmed, it is not yet practical for production web delivery. Keep serving AVIF/WebP with JPEG fallback and monitor.

Responsive Images

• srcset attribute for multiple sizes
• sizes attribute matching layout breakpoints
• Appropriate resolution for device pixel ratios

<img
  src="image-800.jpg"
  srcset="image-400.jpg 400w, image-800.jpg 800w, image-1200.jpg 1200w"
  sizes="(max-width: 600px) 400px, (max-width: 1200px) 800px, 1200px"
  alt="Description"
>

Lazy Loading

• loading="lazy" on below-fold images
• Do NOT lazy-load above-fold/hero images (hurts LCP)
• Check for native vs JavaScript-based lazy loading

<!-- Below fold - lazy load -->
<img src="photo.jpg" loading="lazy" alt="Description">

<!-- Above fold - eager load (default) -->
<img src="hero.jpg" alt="Hero image">

Detected lazy-loader methods (lazy_method field)

scripts/parse_html.py classifies each image's lazy-loading mechanism via the
lazy_method field on every image entry. Five values:

When auditing image SEO, report lazy_method alongside loading so users know
whether their site is using a JS-driven lazy-loader (in which case the native
loading="lazy" attribute is intentionally absent, that is not a regression).

fetchpriority="high" for LCP Images

Add fetchpriority="high" to your hero/LCP image to prioritize its download in the browser's network queue:

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

Critical: Do NOT lazy-load above-the-fold/LCP images. Using loading="lazy" on LCP images directly harms LCP scores. Reserve loading="lazy" for below-the-fold images only.

decoding="async" for Non-LCP Images

Add decoding="async" to non-LCP images to prevent image decoding from blocking the main thread:

<img src="photo.webp" alt="Description" width="600" height="400" loading="lazy" decoding="async">

CLS Prevention

• width and height attributes set on all <img> elements
• aspect-ratio CSS as alternative
• Flag images without dimensions

<!-- Good - dimensions set -->
<img src="photo.jpg" width="800" height="600" alt="Description">

<!-- Good - CSS aspect ratio -->
<img src="photo.jpg" style="aspect-ratio: 4/3" alt="Description">

<!-- Bad - no dimensions -->
<img src="photo.jpg" alt="Description">

File Names

• Descriptive: blue-running-shoes.webp not IMG_1234.jpg
• Hyphenated, lowercase, no special characters
• Include relevant keywords

CDN Usage

• Check if images served from CDN (different domain, CDN headers)
• Recommend CDN for image-heavy sites
• Check for edge caching headers

Output

Image Audit Summary

Prioritized Optimization List

Sorted by file size impact (largest savings first):

Recommendations

1. Convert X images to WebP format (est. XX KB savings)
2. Add alt text to X images
3. Add dimensions to X images
4. Enable lazy loading on X below-fold images
5. Compress X oversized images

Image SERP Analysis

When DataForSEO MCP is available, enhance the image audit with competitive data.

/seo images serp <keyword>

Cross-reference on-page images with Google Images SERP rankings.

Workflow:
1. Fetch Google Images results via serp_google_images_live_advanced (depth=100)
2. Extract: top domains, image types, alt text patterns
3. Output competitor image SERP landscape

Output:

Analysis includes:
- Domain dominance: which sites own the most image positions (top 10 by count)
- Alt text patterns: common title/alt patterns in top-ranking images
- Format distribution: WebP vs JPEG vs PNG in top results
- Opportunity score: keywords where you have page rankings but no image presence

If DataForSEO MCP is not available, inform user and suggest installing the extension.

Image File Optimization

Optimize image files for SEO: format conversion, metadata injection, compression.

/seo images optimize <path>

Optimize image file(s) for web and SEO. Converts to WebP/AVIF, injects IPTC
metadata, compresses, and generates responsive variants.

Tools used (in order of preference):
- exiftool -- EXIF/IPTC/XMP read/write (install: sudo apt install libimage-exiftool-perl)
- cwebp -- WebP conversion (install: sudo apt install webp)
- ImageMagick convert -- Format conversion, resizing (pre-installed on most systems)
- FFmpeg -- Fallback for format conversion (pre-installed)

Before running: Check which tools are available with which exiftool cwebp convert ffmpeg.

Format Conversion

Convert images to modern formats with metadata preservation:

# WebP (recommended default) - with metadata preserved
cwebp -q 82 -metadata all input.jpg -o output.webp

# WebP via ImageMagick (fallback if cwebp not installed)
convert input.jpg -quality 82 output.webp

# AVIF via FFmpeg (slower encode, best compression)
ffmpeg -i input.jpg -c:v libaom-av1 -crf 30 -still-picture 1 output.avif

# Responsive variants (400w, 800w, 1200w)
convert input.jpg -resize 400x -quality 82 image-400.webp
convert input.jpg -resize 800x -quality 82 image-800.webp
convert input.jpg -resize 1200x -quality 82 image-1200.webp

Metadata Injection (IPTC for Google Images Display)

Google Images displays IPTC Creator, Credit Line, and Copyright in search results.
This is NOT a ranking factor but can improve Google Images display and brand attribution.

With exiftool (preferred):

# Read all metadata
exiftool image.jpg

# Inject IPTC + XMP metadata for Google Images rich results
exiftool \
  -IPTC:ObjectName="Product Photo Description" \
  -IPTC:Caption-Abstract="Detailed image description" \
  -IPTC:By-line="Brand Name Photography" \
  -IPTC:Credit="Brand Name" \
  -IPTC:CopyrightNotice="Copyright 2026 Brand Name" \
  -IPTC:Source="brandname.com" \
  -XMP:Title="Product Photo Description" \
  -XMP:Description="Detailed image description" \
  -XMP:Creator="Brand Name Photography" \
  -XMP:Rights="Copyright 2026 Brand Name" \
  image.jpg

# Batch inject to all images in directory
exiftool -overwrite_original \
  -IPTC:By-line="Brand Name" \
  -IPTC:CopyrightNotice="Copyright 2026 Brand Name" \
  *.jpg *.webp *.png

With ImageMagick (fallback):

identify -verbose image.jpg | head -50

convert input.jpg \
  -set comment "Product Photo Description" \
  -set IPTC:2:80 "Brand Name Photography" \
  -set IPTC:2:116 "Copyright 2026 Brand Name" \
  output.jpg

Note: WebP supports EXIF and XMP but not IPTC natively. For WebP files,
use XMP fields instead of IPTC. exiftool handles this conversion automatically.

AI-Generated Images: DigitalSourceType (Merchant Center requirement)

For product images produced by generative AI, Google Merchant Center requires
IPTC DigitalSourceType: TrainedAlgorithmicMedia metadata. This is an
operational policy requirement, not a ranking factor: feeds missing this label
on AI-generated imagery can be disapproved.

Primary source (Merchant Center AI-generated content policy):
https://support.google.com/merchants/answer/14743464
(the ai-optimization-guide does not document DigitalSourceType/IPTC/Merchant labeling.)

Audit command:

# Audit a directory for the IPTC label (counts: missing, ai, captured, etc.)
claude-seo run iptc_ai_label.py audit ./images/ --json

# Audit a single image
claude-seo run iptc_ai_label.py audit ./hero.webp --json

# Inject the AI label into an image
claude-seo run iptc_ai_label.py inject ./ai-hero.webp \
    --source-type trainedAlgorithmicMedia

# Other vocabulary values:
#   compositeSynthetic               (mix of captured + AI elements)
#   algorithmicMedia                 (created purely by algorithm, NOT from sampled training data)
#   compositeWithTrainedAlgorithmicMedia (e.g. AI inpainting/outpainting over real media)
#   digitalCapture                   (fully captured photograph)

Raw exiftool equivalents (for ad-hoc usage):

# Inject manually
exiftool \
  -XMP-iptcExt:DigitalSourceType="https://cv.iptc.org/newscodes/digitalsourcetype/trainedAlgorithmicMedia" \
  ai-generated-product.jpg

# Audit: find images missing the label across a directory
exiftool -if 'not $XMP-iptcExt:DigitalSourceType' \
  -filename -DigitalSourceType *.jpg *.webp *.png

Google extracts these IPTC DigitalSourceType values:
- trainedAlgorithmicMedia: fully AI-generated (use this for diffusion-model
product imagery)
- compositeSynthetic: mixes captured + AI-generated elements
- algorithmicMedia: created purely by an algorithm, not from sampled
training data
- compositeWithTrainedAlgorithmicMedia: composite of trained algorithmic
media + other media (e.g. AI inpainting/outpainting over a real photo)
- digitalCapture: fully captured photograph (note: digitalCapture is not
on Google's extracted-values list, but is a valid IPTC value)

> Provenance signals (consumer-facing): SynthID watermarks and C2PA
> Content Credentials are emerging signals for AI media identification. Treat
> product-surface coverage as subject to change unless verified from a current
> Google-owned source.
> This is detection/transparency, not an extra required Merchant feed field
> beyond IPTC DigitalSourceType.

> Licensable images: to earn the Licensable badge, supply EITHER structured
> data (ImageObject with the license property + acquireLicensePage for the
> "Get this image" link) OR embedded IPTC photo metadata (Licensor URL / Web
> Statement of Rights). Cross-link seo-schema for the ImageObject markup.

> Discovery note: image discovery now includes visual search fan-out
> across Lens / AI Mode / Circle to Search (Gemini multimodal scene/object
> understanding), so images surface via scene, objects, and materials, not alt
> text alone. No new published image-SEO lever yet; keep descriptive alt text +
> clean structured data.

When /seo images optimize is run on AI-generated assets, prompt the user to
confirm the source type and inject the matching IPTC value automatically.

For AI-generated product titles and descriptions, Google Merchant Center
also requires the AI-generated text to be separately specified and labeled in
the feed. This is enforced at the feed layer, not the page layer, flag this
in cross-reference with seo-ecommerce.

Metadata Audit

# Quick audit with exiftool
exiftool -IPTC:all -XMP:all -EXIF:ImageDescription image.jpg

# Batch audit - find images missing IPTC Creator
exiftool -if 'not $IPTC:By-line' -filename *.jpg *.webp *.png

Full Optimization Pipeline

For maximum image SEO, run this pipeline on each image:

1. Audit existing metadata: exiftool -IPTC:all -XMP:all image.jpg
2. Inject IPTC/XMP metadata: Creator, Copyright, Description
3. Convert to WebP: cwebp -q 82 -metadata all image.jpg -o image.webp
4. Generate responsive variants: 400w, 800w, 1200w
5. Verify metadata preserved: exiftool image.webp
6. Generate <picture> HTML: AVIF > WebP > JPEG fallback chain

What Matters vs What Doesn't for Google Images

Error Handling

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