Resize Images is a set of free image tools: resize, compress, convert, crop and image to PDF. Every tool runs inside your web browser. Your images are read, changed and saved on your own device and are never sent to a server, so there is nothing to upload, nothing to wait for and nothing stored anywhere. There is no account, no limit on the number of images and no watermark.
The tools use the image encoders built into your browser, so results can differ slightly between Chrome, Safari and Firefox. Converting iPhone HEIC photos, cropping, creating PDFs and downloading several files as a ZIP load a small open-source library the first time you use them.