For the XMPP interface for the Stack Overflow chat, I am currently taking the HTML of the chat messages and converting to valid XML, and setting that as the html
ch
Adium, iChat and Pidgin all support XEP-0231, which allows you to send the provide binary data, including images to this purpose. Basically, it allows you to specify a unique identifier as the source for an image, and then the other client can decide if he wants to request the data in a
request.
I've been working with this in python's Twisted, but meeting with some frustration. I do know that Adium and iChat at least use it to request the data.