This might need an update for Windows 8. Not that it doesn't work (I call it at least a dozen times when I run my workstation build process) but it may not set/delete the new
Metro interface. Apparently, the DELETE option is CRITICAL!! \:\) So - Microsoft really thought we needed a new app to put a picture on the screen?

The general form of Associate is Extension, Identifier, Description, App to Open, App to Edit.
 Code:
$Open = '%SystemRoot%\System32\rundll32.exe "%ProgramFiles%\Windows Photo Viewer\PhotoViewer.dll", ImageView_Fullscreen %1'
Associate('.jpg', 'jpegfile', 'JPEG Image', $Open, 'mspaint.exe %1')
should work. DO NOT change the extension or short-name as these are already defined in Win-8. You'll want to modify the current settings. Also, since the command now includes a comma AND quotes, you'll need to use the $Open to insure that the quotes and comma are treated as a single parameter. You don't need the last arg if you don't want a Right-Click/Edit option, or you can set it to some other editor.

You can find this info in the registry.. in this example, search HK_Classes_Root for the extension. In the OpenWithProgids key, find the REG_SZ string (will be empty!) - this is the name of the key to locate in the same hive. It's "jpegfile" in this case. Expand "jpegfile", then "shell", then "open" and find "command". The default value contains the executable command to launch the associated app. If you defined an Edit association, then an "Edit" section similar to "open" will exist.

Please grab the latest UDF version from my web site. Let me know how this works for you.

Glenn
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Actually I am a Rocket Scientist! \:D