Thumbnails of pictures, office documents, and folders exist in a database called the thumbcache. Each user will have their own database based on the thumbnail sizes viewed by the user (small, medium, large, and extra-larger
C:\%USERPROFILE%\AppData\Local\Microsoft\Windows\Explorer
These are created when a user switches a folder to thumbnail mode or views pictures via a slide show. As it were, our thumbs are now stored in separate database files. Win7+ has 4 sizes for thumbnails and the files in the cache folder reflect this:
32 -> small - 96 -> medium
256 -> large - 1024 -> extra large
The thumbcache will store the thumbnail copy of the picture based on the thumbnail size in the content of the equivalent database file.