Save the file as ActivateViewer.reg (ensure the extension is .reg and not .txt ). Keep this file on your USB drive.
Create a text file named restore_photo_viewer.reg and paste the following: microsoft photo viewer download for windows 81 portable
There is no official microsoft photo viewer download for windows 81 portable package provided by Microsoft. Any website offering a standalone .exe or .zip file claiming to be the original Windows Photo Viewer is: Save the file as ActivateViewer