The above replies were meant for Exchange Server 2010, and not for Exchange Server 2007. As far as I know, you cannot do this in the Exchange Server 2007. Pictures from GAL (global address list) is only supported in Exchange server 2010 and upwards.
However, you can do this in Exchange Server 2007 using third-partty utilities or powershell scripts. My IT friend referred me to Steve Goodman's blog where Steve mentions about a powershell script that he has written specific to Exchange Server 2007
And if you need any info on the "thumbnailphoto" attribute of a user object in the active directory, please refer the Microsoft Support article titled "How To Manipulate the ThumbNailPhoto Attribute of a User Object in the Active Directory". You can find the article @
Hope this helps.