ihateimg.cv offers a set of image tools that run on your own device. Because nothing is sent to a server, there is no file size limit, no watermark and no sign-up.
Tools cover format changes such as HEIC to JPG or PNG, WebP to JPG and JPG to PNG, as well as compressing, resizing and cropping. Batches of any size are supported, which is handy for converting iPhone photos in one go.
