How To: Repair thumbnail image preview in Windows Explorer

Applies to: Windows 98, Me


The ability to view graphics files as thumbnail images no longer works.


Windows 98 introduced the capability to preview graphics files as thumbnail images when the folder is viewed as a web page. This capability can become disabled if graphics applications are installed which change the Registry associations for graphics file types. Applications that are known to cause this problem include Corel Draw up to at least version 9.

It isn't possible to restore the thumbnail functionality by simply changing the association back to one of the standard Windows graphics programs. The thumbnail images are displayed using a Windows feature called a "shell extension". The loss of the association with this extension can only be repaired by direct modification of the Registry.

Further information

All file types have a Registry key under HKEY_CLASSES_ROOT named for their extension (for example .jpg). This key has a default value (for example, jpegfile) called the "progid" that links it to another Registry key containing information about the programs used to open the file, and other associated actions.

If there is a shell extension associated with this file type, the file extension key has a sub-key named ShellEx. Shell extensions can be used to do a great many things, such as add special items to a file type's context menu.

If a file type can be displayed by Explorer in a thumbnail view, the ShellEx key will contain a sub-key named {BB2E617C-0920-11D1-9A0B-00C04FC2D6C1}. This gobbledygook is a globally unique identifier (GUID) used to indicate a thumbnail preview shell extension. The default value of this key contains another GUID that links it to the software component responsible for displaying the thumbnail preview. In the case of the default thumbnail preview feature provided by Windows, that value is {7376D660-C583-11D0-A3A5-00C04FD706EC}. The file types supported by Windows are: .art, .bmp, .dib, .gif, .jfif, .jpe, .jpeg, .jpg, .png and.wmf .

Note that using this mechanism, other applications can supply additional shell extensions to extend the thumbnail preview facility to include other file types. Examples include QuickView Plus and Microsoft Office.

How the ShellEx entry for an image file type should look in the Registry Editor


To reinstate the facility, you must ensure that the Registry key for each affected file type contains a ShellEx folder named {BB2E617C-0920-11D1-9A0B-00C04FC2D6C1}, containing a default value of {7376D660-C583-11D0-A3A5-00C04FD706EC}.

Although it's possible to do this by hand, it isn't easy. Instead, download the file thumbnail.reg to your hard disk. Open the file in a text editor to see that it looks alright. It should be fairly obvious what it will do. Then right-click the file and select Merge from the context menu. This will add or repair the Registry values necessary for the thumbnail feature to work.

Warning: You should use ScanReg to back up your Registry first, and know how to boot to DOS from an emergency recovery disk and restore from this backup in the unlikely event that merging this file causes a problem with your computer. You carry out this advice at your own risk, and we accept no responsibility for any problems that might be caused.

Note that the applications which caused the loss of the default thumbnail preview may also have disabled this facility in respect of other file types for which shell extensions have been added by other software such as Microsoft Office, as mentioned above. There are too many variables to provide a safe, generic fix. For example, we do not know what application may be on a computer, what the correct GUID is, or which file types are affected (the user may have chosen not to install all of the available file filters when the application was installed.) If you believe that this has occurred, the only solution we can suggest is to reinstall the application that added the extra thumbnail previews.