Just to be clear, this picture is only visible to those inside of your organization or other organizations that you are federated with.
Outlook relies on Active Directory to pull these pictures from and present them to end users. There is an attribute in AD called
ThumbnailPhoto that stores these pictures. You can always ask your administrator to remove or change the picture associated with that AD user account if you do not have access yourself to these settings. The following set of instruction are taken from here.
How to import photos to AD
There is a minor schema change required to enable use of photos in AD. The change is to flip the thumbnailPhoto attribute to make it replicate to the Global Catalog. Exchange 2010 Service Pack 1 (SP1) automatically performs this schema change, so if you have deployed Exchange 2010 SP1, you do not need to make a schema change. Otherwise, you do need to follow these steps:
If you haven’t registered the Schema MMC snap-in on the server you want to make this change on, go ahead and do so using the following command: Regsvr32 schmmgmt.dll
Open an MMC console (Start | Run | MMC) and add the Schema snap-in.
In the Active Directory Schema snap-in, expand the Attributes node, and then locate the thumbnailPhoto attribute.
In the Properties page, select Replicate this attribute to the Global Catalog, and click OK.
Then you are ready to import photos into AD. This is done with a Powershell command.
Import-RecipientDataProperty -Identity "Dollie Madison" -Picture
-FileData ([Byte]$(Get-Content -Path "C:\pictures\DollieMadison.jpg" -Encoding Byte -ReadCount 0))
The recommended thumbnail photo size is 96×96 pixels, and by default, the maximum size of photo that can be imported with the Import-RecipientDataProperty command is 10-KB. There are also options to force inclusion of the photo in the offline address book, see the ‘links for more information’ below on how to make those and other advanced changes related to AD photos.
Here is another resource for updating your Active Directory photo's.