This feature is very demanding on the performance of your device. And strongly depends on the size of the processed image. Optimization reduces the performance requirement, but also reduces image quality. If the performance of your device is not enough, the program may produce errors. During image processing, your browser can noticeably slow down. Internet Explorer is not supported.
If the download doesn't start automatically, to save the picture, open (on PC - right-click on the photo, on mobile devices with touch screen - touch the photo and hold it there until the menu pops up) the context menu and select the appropriate option ("Save ...").