MysticThumbs is described as 'Generates thumbnails of many image types not natively supported by Windows. It does this transparently and in the background for Explorer so you don't have to run a separate application to preview your images' and is an app. There are more than 10 alternatives to MysticThumbs for Windows, File Explorer, F-Droid and Android. The best MysticThumbs alternative is SageThumbs, which is both free and Open Source. Other great apps like MysticThumbs are Icaros, Smart SVG Viewer, SVG Explorer Extension and SVG Shell Extensions.
This application for android devices searches for pictures (JPEG) on your device and adds a thumbnail if they don't have one yet. Thumbnails are added to the EXIF metadata structure.
