If your email signature includes a picture and this picture will not show on the target email program, you have to add the following registry entry:

HKEY_CURRENT_USER\Software\Microsoft\Office\<Version>\Outlook\Options\Mail

Change the <Version> string to one of the following number:

• Microsoft Outlook 2007: 12.0
• Microsoft Outlook 2010: 14.0
• Microsoft Outlook 2013: 15.0
• Microsoft Outlook 2016: 16.0

Create a new DWORD (32-bit) Value called Send Pictures With Document with value 1