Many online application, admission and recruitment forms limit the photo and signature uploads to 20 KB or less, and a phone photo of several megabytes is far over that. This page opens with the target set to 20 KB, so you drop the image and compress. The tool first lowers the JPG quality, keeping it as high as the limit allows, and if the file is still too big it scales the image down and tries again, so the result is as sharp as a 20 KB file can be. For a portrait photo that usually ends up somewhere around 250 to 350 pixels on the long side. Check the form for dimension rules as well as file size: some ask for a specific width and height in pixels or centimetres, in which case resize to those dimensions first with Image Resizer and then compress here, since a smaller image needs less compression and looks better. Use a plain light background and even lighting, because flat areas compress far better than busy ones. The target is counted as 20,000 bytes, which stays under the limit whether the form means 1,000 or 1,024 bytes per kilobyte. For a signature only see Compress Image to 10KB, and for a less strict limit Compress Image to 50KB.
Image compression is one of the highest-impact performance optimizations for most websites. Images typically account for 50 to 80 percent of a page's total download size, and unoptimized images are the most common cause of poor Core Web Vitals scores, particularly Largest Contentful Paint (LCP). A JPEG compressed to 75 percent quality is visually indistinguishable from the original for photographic content in most contexts, but can be 60 to 70 percent smaller. The human eye is much more sensitive to sharpness and color accuracy in certain areas (faces, text in images, sharp edges) than in others (smooth backgrounds, sky, blurred backgrounds). Lossy compression algorithms exploit this by applying heavier compression in less sensitive areas. For PNG files, lossless compression reorders pixel data and uses more efficient encoding tables. PNG compression level (1-9) trades CPU time for file size: higher levels take longer to encode but produce smaller files. For web use, both JPEG and PNG should be served at their maximum practical compression level (JPEG 75-85, PNG level 9) since the decompression time is negligible but the smaller network transfer size benefits every user. The recommended modern workflow for web image delivery is: optimize your original image with this tool, then serve it in WebP format for Chrome and Safari 14+ users with a JPEG fallback for older browsers using the HTML picture element with source type="image/webp".
Read our guide: In-depth guide for Compress Image to 20KB