Contact picture displayed in e-mail header
All e-mail messages received from a contact for which you have a picture will display the contact’s picture to the right of the message header. To disable this feature, deploy the following registry data:
Key: HKCU\Software\Microsoft\Office.0\Outlook\Options\Mail
DWORD: ShowContactPicture
Values:1 (or missing DWORD) = show contact picture if available
0 = do not show contact picture
Portanto, você pode verificar se o valor dessa entrada do registro é 1 ou tentar excluí-lo.
Uma informação um pouco conflitante da Adicione, altere ou remova uma foto para um contato :
If both the sender and the recipient are using Office Outlook 2007, a contact picture is displayed in messages received if the sender uses a contact photo. The picture appears in the message header [...] You can double-click the contact picture to open the contact or right-click it for other contact options.
Note : For the picture to display, the contact must also be saved in an Outlook Contact folder and that Contact folder must be designated as an Outlook Address Book (Outlook Address Book: An address book that is automatically created from contacts in the Contacts folder. The contacts can be people inside and outside of your organization. When you update your contacts, the Outlook Address Book is updated as well.). These are the default settings when creating contacts in Microsoft Outlook. If you don't see the picture included with a contact, check to see if the default settings have been changed.