About the Thumbnail Handler
Beginning with Windows 98, Windows Explorer has allowed you to view thumbnail images of files on your computer. File formats such as HTML documents, PowerPoint presentations, and various image types including JPEG, GIF, and BMP images, are supported out of the box with Windows.
Microsoft allows third parties to develop thumbnail handlers, which provide Windows Explorer with thumbnails for additional file formats. PSP Thumbnail Handler provides Windows Explorer with thumbnails for Paint Shop Pro file formats. All PSP files, such as images, picture tubes, and frames, share a common file format and are supported by PSP Thumbnail Handler.
Thumbnails are visible in Explorer's thumbnails view, as well as on the left side of the window when a given file is selected.