I am not sure about the graphic. Have you tried creating the signature as a signature and apply that signature to the account you want to use? The following macro version will use the named account (shown here as "account name"
Code:
Sub PersonalMessage()
Dim oItem As Outlook.MailItem
Dim oAccount As Outlook.Account
Const strAcc As String = "account name"
Const strFolder As String = "D:\Word 2010 Templates\"
Const strFilename As String = "Example.oft"
For Each oAccount In Application.Session.Accounts
If oAccount.DisplayName = strAcc Then
Set oItem = Application.CreateItemFromTemplate(strFolder & strFilename)
oItem.BodyFormat = olFormatHTML
oItem.SendUsingAccount = oAccount
oItem.Display
End If
Next oAccount
Set oItem = Nothing
End Sub