Explorer Thumbnails in the Registry

Windows Explorer will show thumbnails for certain file types when browsing a folder. The information for which file types to show a thumbnail for and what DLL to use is stored in the registry.

HKCR\ – shows a list of file extensions.  Underneath each file extension’s key may be another key called ShellEx that contains thumbnail information, although this is not always true.  For example, .png contains no ShellEx key, but still shows thumbnails in Explorer.
Underneath the ShellEx key should be another key named “{BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}”, whose default value is another class ID (the long string of numbers surrounded by curly brackets).  That class ID points to something in HKCR\CLSID\{whatever}.  That key will contain a reference to the DLL used for thumbnails for that file type.

Alongside “{BB2E617C-0920-11d1-9A0B-00C04FC2D6C1}” may be another key called “{FFB699E0-306A-11d3-8BD1-00104B6F7516}”, which for me seems to be an nVidia key for something-or-another.