The jitsi client does not support images embedded using the data URI scheme in HTML-IM used in chat. It would be great if it could do so. (It's a very simple URI scheme.)
To test this, you can befriend email@example.com<mailto:firstname.lastname@example.org> for example. You need to notify me (email@example.com<mailto:firstname.lastname@example.org>), so I can approve the request. It's a sensor you can chat with. Just send "html+" to enable HTML, and "??" to perform a large readout. This will return current values, but also historical values, in the form of graphs. Jitsi seems to understand the <img> tag, but does not seem to understand the data URI scheme.
Is it possible for somebody to look at this? In that case, I would mention Jitsi as a recommended tool and demonstrate it in the book I'm currently writing ("Learning Internet of Things"), in the chapter concerning XMPP.