What happened to Windows picture and Fax Viewer?

What is the file name and extension for Windows picture and fax
viewer? I want to use it for an OLE object to view pictures.

and

How do I change my default image viewer back to the Windows
Picture and Fax Viewer?

Turns out it’s easier to get rid of than it is to restore. But not
impossible.

It took a little spelunking using Process Explorer to determine the command line that is used when
Windows Picture and Fax Viewer is invoked. Turns out that it’s not a
stand-alone exe at all.

The command to run Windows Picture and Fax viewer is:

rundll32.exe
C:\WINDOWS\System32\shimgvw.dll,ImageView_Fullscreen
path-to-picture

So, to answer the first question: shimgvw.dll probably exposes the objects
needed to use Windows Picture and Fax Viewer as an OLE object.

As for the second, restoring Windows Picture and Fax Viewer as the viewer
for images:

• Note what file extension you want to change the default for. That’s the
  “.jpg”, “.gif”, and so on at the end of the filename. It indicates the type of
  picture, and more importantly, it’s what Windows uses to decide what program to
  use to display it.
• Open up Windows Explorer. (The Windows Key + E, on many keyboards.)
• Find any file with that same extension.
• Right-click on the filename, and select Open With
  ….
• Select Choose Program at the bottom of the list that’s
  displayed.
• In the resulting dialog box, “Windows Picture and Fax Viewer” should
  already be listed. Click on it.
• Check the box labeled “Always use the selected program to
  open this kind of file”.
• Press OK

If for some reason it’s not already in the list, you can force the
association by following these steps, still in Windows Explorer:

• On the Tools menu, click Folder
  Options…
• Click on the File Types tab.
• Scroll down to the extension you care about, for example “JPG”.
• Press the Restore button, if it exists.
• Press the Advanced button.
• Click on the Open action.
• Click on Edit…
• In the Application used to perform action: enter
  C:\WINDOWS\system32\rundll32.exe
C:\WINDOWS\System32\shimgvw.dll,ImageView_Fullscreen %1. Where
  “C:\WINDOWS” is the directory containing your Windows installation.
• Press OK

You’ll want to repeat that for every extension (GIF, JPG, JPEG, etc.) for
which you want to change the behavior.

Update: Another approach to re-installing
Windows Picture and Fax Viewer
is to click on Start, Run… and type in:

regsvr32 /i shimgvw.dll

and press OK. Then press OK again on the resulting success message.
(Thanks to comment poster Leon for this suggestion.)