Change BMP Icons to Thumbnail View
Open the Registry Editor (Start/Run and type REGEDIT in the Run box). Drill
down (by clicking on the plus signs) into HKEY_CLASSES_ROOT\Paint.Picture\DefaultIcon. Double-click on the word "Default"
in the right pane. Copy the contents and paste them into a file (or write
the contents down on paper) just in case you want to reverse what you are
about to do. Now replace the value with %1 (a percent sign and the number
one). Click on OK and close the Registry Editor. After rebooting your system,
you'll notice that the icons of BMP files are now thumbnails of the images
in the files.