Image SEO is the practice of optimizing images on a web page so that they contribute positively to search engine rankings, page performance, and accessibility. While images are primarily a visual medium, search engines cannot interpret them the way humans do, which means every image on a page requires deliberate configuration to be understood, indexed, and ranked effectively.
Alt Text and File Naming
The most fundamental element of image optimization is the alt attribute, also called alt text. This short description is embedded in the HTML image tag and serves two purposes: it tells search engine crawlers what the image depicts, and it provides a textual fallback for users who rely on screen readers. Descriptive, specific alt text that reflects the image content and the surrounding page topic is far more effective than generic placeholders like "image1" or an empty string.
File naming follows the same principle. A file named red-running-shoes-womens.jpg communicates meaningful context to crawlers, whereas IMG_4821.jpg does not. Using lowercase letters and hyphens to separate words is the widely accepted convention for image file names.
Format Selection and Page Speed
The format in which an image is saved has a direct impact on file size and therefore on page load speed, which is a confirmed ranking factor. Modern formats such as WebP and AVIF deliver significantly smaller file sizes compared to legacy formats like JPEG or PNG, without a meaningful loss in visual quality. Serving images in the appropriate modern format is one of the most impactful technical changes a site can make for both performance and SEO.
Beyond format, lazy loading defers the loading of off-screen images until a user scrolls toward them, reducing the amount of data transferred on initial page load. Combined with responsive images, which serve different image sizes depending on the user's screen and device, these techniques help meet the performance thresholds measured by Core Web Vitals, particularly Largest Contentful Paint (LCP) when a hero image is the primary visual element.
Structured Data for Images
Structured data, implemented via Schema.org markup, allows publishers to provide explicit metadata about images to search engines. When applied correctly, it can enable rich results in Google Search, such as image carousels for recipes, products, or articles. For e-commerce sites in particular, product image structured data can improve visibility in Google Images and Shopping surfaces.
How Images Affect Rankings
Images influence search rankings both directly and indirectly. Directly, well-optimized images can rank in Google Images, which represents a meaningful source of organic traffic for visual industries such as fashion, food, and real estate. Indirectly, poorly optimized images slow down page load times, which degrades user experience signals and can suppress rankings in standard web search. A holistic image SEO strategy therefore treats visual assets not as decorative elements, but as indexed content and performance variables that require the same attention as text.