Sure. Remove the images from your contacts.

It also picks them up from social connector providers you are using.
You can set a reg key - this affects the display of contact photos in the header of email messages, in the people pane, and the Outlook contact card.
Key: HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Common
DWORD: TurnOffPhotograph
Values:
1 = Contact photos are not displayed in the People Pane. If you are using Outlook 2010, they are also not displayed in the header of email messages and the Outlook contact card
0 = The Outlook Social Connector displays contact photos in the People Pane.