How to Optimize Images for Websites (Speed and SEO)
Images are usually the single biggest contributor to a slow-loading web page, and page speed is both a direct user-experience factor and a known input into how search engines rank pages. Optimizing images properly is one of the highest-leverage, lowest-effort improvements available for both.
Match the file's dimensions to its actual display size
The most common and most wasteful mistake is uploading a full-resolution photo — often several thousand pixels wide, straight from a camera or phone — when the image will only ever be displayed at a few hundred pixels on the actual page. The browser still has to download the entire oversized file even though it's displaying it much smaller. Resizing an image to roughly match its largest actual display size (accounting for high-density "retina" screens, which need somewhat more pixels than a 1:1 match) is usually the single biggest win available.
Choose format based on content, not habit
Photos generally belong in JPG or, better, WEBP, which typically achieves a smaller file size than JPG at equivalent visual quality and has broad browser support today. Graphics with sharp edges, text, or transparency (logos, icons, illustrations with flat colors) belong in PNG or SVG rather than JPG, since JPG's compression blurs exactly the kind of sharp detail those images rely on. Defaulting every image to PNG "to be safe" is a common habit that costs real file size on anything photographic.
Compress everything, even after resizing
Resizing and compression solve different parts of the same problem and should both be applied — a correctly-sized image at an uncompressed or lightly compressed setting still carries more data than it needs to. A moderate-to-high quality compression setting (enough to be visually lossless at normal viewing size) on top of correct sizing gets the meaningful majority of available savings.
Why this affects search ranking, not just user experience
Page load speed is a measurable, known factor search engines use in ranking, and large, unoptimized images are one of the most common causes of a slow page. Beyond the ranking signal itself, a faster-loading page also means visitors are less likely to leave before it finishes loading — which matters for search performance indirectly too, since high bounce rates are a signal search engines take into account.
Don't forget alt text
While it's not a file-size or speed issue, descriptive alt text on every image is a genuine, low-effort SEO input — it tells search engines what an image actually depicts, which is content they otherwise can't directly read from the pixels themselves.
Resize Image and Compress Image together cover the two biggest levers for web image performance, both directly in your browser. The image converter handles switching to a more efficient format like WEBP when that's the bigger opportunity for a given image.