Thumb.db is is a cache of the current picture in that directory.to remove it go for following step1 > open "WINDOWS EXPLORER".2>go to "TOOLS".3>open "FOLDER OPTIONS".4>go to "VIEW".5>see 1st section "FILES & FOLDERS".6>click on the "DO NOT CACHE THUMBNAILS".now the thumbnail file will be removed from ur computer once u do this the file will be never created.