Thumbs.db is a file created by Windows when thumbnail view is used. It is a hidden file not viewed by most users and not updated when files are moved from a folder which images have passed through or deleted. This gives a secondary chance that someone will leave behind at least partial evidence of an image in their Windows folders.
There is a forensic open source application developed at sourceforge called vinetto at http://sourceforge.net/projects/vinetto that can extract them. It does require a python environment. Additionally, there are several other Java solutions based around the Jakarta project that is apart of Apache. Additional resources about thumbs.db can be found in a white paper at http://www.accessdata.com/media/en_US/print/papers/wp.Thumbs_DB_Files.en_us.pdf.
MiTeC Windows File Analyzer  is a tool for forensic analysis of Thumbnail Databases, Prefetch files, shortcuts, IExplore Index.DAT files and Recycle Bin contents on a Windows system. It will print a report of analyzed files.
See Vista thumbcache
Thumbs.db no longer exists in Vista/7 as individual files. This data has been moved to a centralized database located in \Users\%username%\AppData\Local\Microsoft\Windows\Explorer
In Windows 7, thumbs.db files are not created under normal usage when a user browses a folder in explorer. However, they are created if the same folder is browsed through its network path such as via \\localhost\c$. These files do not follow the xp thumbs.db format. The format is still an OLE container but without the Catalog stream and with a few other changes.
In Windows 8 and 8.1, both thumbcache and thumbs.db are present. Thumbs.db will only be created in folders which reside under a user profile folder (C:\Users\USERNAME\*). But accessing other folders using their network paths such as \\localhost\c$ will create thumbs.db in other folders as well. The format of these thumbs.db files is the same as Windows 7 thumbs.db.