A picture saved from a website may arrive as WebP even though its content looks like an ordinary photograph. An older editor or a restrictive form might ask for JPG instead. A real conversion decodes that picture and writes a JPEG; simply changing the filename extension leaves the underlying WebP data unchanged.
Before converting a downloaded image, confirm you have the right to reuse it. Also check whether the website offers a higher-resolution original. A small preview image remains small after conversion, and visible watermarks remain part of the picture. The converter does not fetch images from a URL, remove a watermark or recover a hidden original. Choose the file already saved on your own device and keep a copy of it.