Do you, or anyone, have [links to] more information about exactly what Outlook does when requesting a tracking pixel to display in an email. I can't sniff it (

Do you, or anyone, have [links to] more information about exactly what Outlook does when requesting a tracking pixel to display in an email. I can't sniff it (Wireshark) as I don't have that sort of access to a network with Outlook on. I've googled but didn't find anything useful.