HTML signatures in Outlook 2013 or Outlook 365 no longer convert and embed pictures. Instead, a URL to the picture source is used.  The result is, though all looks well when composing a message, the recipient won’t see the picture unless it is online somewhere and available via a standard URL.  Locally stored and referenced pictures will not be visible because, to the recipient, a reference to the sender’s C drive means nothing.

To revert to the behavior of previous versions of Outlook, where images are converted and sent with the message, add the following registry key:

Key: HKEY_CURRENT_USER\Software\Microsoft\Office\15.0\Outlook\Options\Mail
Value type: REG_DWORD
Value name; Send Pictures With Document
Value: 1