Image SEO: ALT Tags, File Names, Image Search Traffic

Chapter 4: Content Marketing · Question 58

You may not have noticed, but Baidu Image Search handles hundreds of millions of queries every day (industry estimate). For many websites, image search traffic can account for 10%-20% of total traffic (industry estimate, not official statistics), especially for e-commerce, home, food, and travel sites. Yet most site owners haven't even written the most basic ALT tags properly. Image SEO is an optimization item with an extremely high return on investment—small changes, fast results, and little competition.

Why is image search worth pursuing?

Traffic characteristics of Baidu Image Search:

• High precision: Users searching for "Nordic-style living room renovation renderings" have very clear purchase intent
• Low competition: Most websites neglect image optimization, so a little effort can get you to the top
• Extra traffic: It doesn't take up ranking slots in text search—it's pure incremental traffic
• Baidu image recognition: Baidu's reverse image search displays the source page of images, so high-quality original images can drive referral traffic

How to write ALT tags correctly

ALT (Alternative Text) is the core basis for search engines to understand image content.

Incorrect example:

<img src="1.jpg" alt="">
<img src="product.jpg" alt="图片">
<img src="sofa.jpg" alt="沙发沙发沙发北欧沙发客厅沙发">

Correct example:

<img src="nordic-grey-sofa-living-room.jpg" 
     alt="北欧风格灰色三人布艺沙发客厅实景图">

ALT tag writing rules:

File naming conventions

Search engines parse image file names as an auxiliary signal:

• ✗ IMG_20240<a class="ilink" href="/100wen/https-301-404-handling/">301</a>_001.jpg(default camera naming, meaningless)
• ✗ 未命名.png(Chinese file names get encoded into garbled characters in URLs)
• ✓ beijing-team-building-outdoor.jpg(descriptive English + hyphen-separated)
• ✓ yunnan-dali-erhai-lake-sunset.jpg(location + scene + feature)

Naming formula:[主题]-[描述]-[特征].格式

Image formats and compression

Recommended compression tools: TinyPNG, Squoosh (by Google), Zhitu (by Tencent, optimized for domestic CDNs).

Goal: Keep each image under 100KB; above-the-fold hero images no larger than 200KB.

SEO impact of lazy loading

Lazy loading can speed uppage speed, but improper implementation can prevent search engines from crawling images:

• Recommended solution: Use the native loading="lazy" attribute, which Baidu Spider can correctly recognize
• Avoid this approach: Pure JavaScript dynamic image loading (src written in a data attribute), which spiders may fail to crawl
• Compromise solution: Do not lazy-load above-the-fold images; use lazy loading below the fold

Image Sitemap

When searching for the sitemap Declare image information separately in the sitemap to help search engines discover and index them:

<url>
  <loc>https://example.com/decoration-guide</loc>
  <image:image>
    <image:loc>https://example.com/images/nordic-living-room.jpg</image:loc>
    <image:title>北欧风客厅装修效果图</image:title>
    <image:caption>15平米小户型北欧风格客厅设计方案</image:caption>
  </image:image>
</url>

Structured data markup

Using Schema.org's ImageObject markup can give images rich media display in search results:

• Product images → in Product schema's image property
• Recipe images → in Recipe schema's image property
• Article images → in Article schema's image property

CDN considerations

• Ensure the CDN domain is accessible to Baidu Spider (some overseas CDNs are unstable when accessed domestically)
• Keep image URLs stable; do not frequently change CDNs, which causes URL changes
• Recommend using your own subdomain (e.g., img.example.com) rather than the CDN's default domain, which helps brand consistency

Practical recommendations

• Can do immediately: Check the ALT tags of all images on the site, batch-scan with an "empty ALT detection tool", and prioritize fixing the 20 pages with the highest traffic
• Prioritize original images: Baidu Image Search gives weighting to original images, especially real-life photos and original design images, which have a clear ranking advantage over stolen stock images
• Pay attention to Baidu Image Search's "filter tags": Baidu image results have color, size, and type filters at the top; ensure your image metadata is accurate so your images appear in the corresponding filter results