Image SEO
The practice of optimizing images on a webpage for search engines and Google Images, including alt text, file names, compression, and structured data.
Image SEO is the practice of optimizing the images on your webpages so they rank well in Google Images and contribute to the parent page's relevance and ranking in traditional web search. It encompasses several distinct techniques, each with measurable impact.
The most important element is alt text — the descriptive text added to an <img> tag that screen readers read aloud and search engines use to understand the image's content. Per Google's own image SEO documentation, descriptive, specific alt text is a direct ranking factor for Google Images. Other key elements include descriptive file names (cat-on-windowsill.jpg is far better than IMG_4523.jpg), compressing images for page speed (Google's Core Web Vitals give LCP priority to image-heavy pages, and uncompressed images are the #1 cause of LCP failures per the 2024 HTTP Archive Web Almanac), using modern formats like WebP and AVIF (average 30-50% size reduction vs JPEG/PNG), responsive images with srcset, and ImageObject schema markup for rich results.
The traffic upside is significant. Per SparkToro's 2024 analysis, Google Images is the entry point for ~22% of all web searches, and pages that rank well in Google Images average 12-35% more organic traffic than pages with comparable traditional rankings but poor image optimization. For e-commerce sites, the impact is even larger — a 2023 Baymard study found product image quality is the #1 factor in purchase decisions online.
Best practices: write descriptive alt text (5-125 chars, context-specific), use descriptive file names, compress to under 100KB for product images and 30KB for thumbnails, serve WebP/AVIF with JPEG fallback, add ImageObject schema for important images, lazy-load below-the-fold images, and never use images as the primary content delivery method (text + image is faster and more accessible than image alone).