ThumbnailPhoto

Active Directory supports storing small user photos directly in the database.
The ADSI attribute is 'thumbnailPhoto' and has been around since Windows 2000, but wasn't really used until Exchange/Outlook 2010.

You can also use this image to set the Windows 7 logon image by using the following utility as a login script. http://jacob.steenhagen.us/blog/2012/02/loading-a-windows-7-user-tile-using-the-picture-in-active-directory/

References

http://jacob.steenhagen.us/blog/2012/02/loading-a-windows-7-user-tile-using-the-picture-in-active-directory/

http://joco.name/2010/12/06/i-discovered-the-new-windows-user-tile-api/