Windows 7 Home Premium:
Open the registry (regedit.exe) from the Run command and navigate to the following key:
Double click on the DisableThumbnailCache key in the right-hand pane and change the value to 1. If the key is not there, go to Edit, then New and choose DWORD Value to create one with the same name.
Windows 7 Professional:
There are a couple of ways to turn off caching of thumbnails, one includes editing the registry and the other includes using the Local Group Policy Editor. I have edited the registry a million times and don’t mind doing that, but it doesn’t get any easier than using the Local Group Policy Editor. The first step is to log on to Windows 7 as an administrator. To start the Local Group Policy Editor, click the Windows 7 start icon and type gpedit.msc in the search text box and hit Enter. The Editor will open to the top-level Local Computer Policy, so you will have to expand the User Configuration item in the left-side pane of the Editor window. Drill down through Administrative Templates, then Windows Components, and click on the Windows Explorer item. Near the top of the list in the right-hand pane of the Editor window you will find the setting “Turn off the caching of thumbnails in hidden thumbs.db files” (see below).
To edit this policy setting, either double-click on the title of the policy or click the link titled “Edit Policy Setting” to the left of the setting list after you select the policy. It is interesting to note that below the Edit Policy Setting link it indicates that the requirement is Windows Vista Service Pack 1. To change the policy, merely check the “Enabled” radio button and click OK (see below).
Close the Local Group Policy Editor and you will notice that all of those thumbs.db files have disappeared.