Use a browser-based image compressor that lets you dial in the quality level and re-encodes the picture on your device. It reduces the file size for web or email while keeping the image sharp, and it never uploads your photo to a server.
Image compression trades a little visual detail for a much smaller file. The trick is that JPEG and WebP can drop a lot of data before your eye notices, so a quality setting around 70 to 85 percent typically cuts the file size dramatically while looking identical at normal viewing size. A tool that shows the before and after size lets you find that sweet spot.
Because the compression happens in your browser, your original photo is never uploaded. That is important for personal pictures, product shots you have not published yet, or screenshots that contain sensitive information.
At a sensible quality level the difference is invisible at normal size, while the file gets much smaller.
No. The image is compressed locally in your browser and never sent anywhere.
Common web formats like JPEG, PNG and WebP work directly in the browser.