Image Optimization is the practice of reducing image file size and improving delivery so pages load faster without an unacceptable loss of visual quality.
The core levers are format, compression, dimensions, and loading strategy. Modern formats like WebP and AVIF deliver smaller files than JPEG or PNG at comparable quality. Serving images at the dimensions they actually display, rather than scaling huge originals down in the browser, avoids wasted bytes. Responsive images using srcset and sizes let the browser pick an appropriately sized file for each device.
Delivery technique matters as much as the file itself. Lazy loading defers off-screen images so they do not block the initial render, while the largest above-the-fold image should usually load eagerly because it is often the Largest Contentful Paint element, a Core Web Vital with a good threshold of 2.5 seconds or less. A content delivery network and proper caching headers further cut load time. Explicit width and height attributes prevent layout shift as images load, which protects Cumulative Layout Shift.
Image optimization is mostly a performance discipline. The broader work of making images findable and understandable, covering alt text, file naming, and image sitemaps, falls under image SEO, which is a related but distinct concern.
Related: Image SEO, LCP Complete Guide, CLS Complete Guide
Claude Vincent is a technical SEO consultant focused on crawlability, rendering, and AI-search visibility. He writes the field guides and case studies at SEO ProCheck, with a bias toward the durable, unglamorous work that decides whether search engines and AI answer engines can actually read and cite a site.
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