A lot has been written about using Ink for sending pictures in the past years (since Ink was available). So you might wanna search the forums with
" Ink" regarding this. Bottom line is that this is far from easy to do. Scripts in Messenger Plus! Live also don't have any access to the needed stuff for doing this, as such you'll need external DLLs and you need to make an engine which sends Ink on protocol level.
As for using LaTeX, this also has been a topic since years and years. Many tools, plugins, etc have been released for doing this. For pulling this off with scripts you have almost the same problems as explained in first paragraph (since it also involves sending images).
You are far better of making a Messenger Activity, which are small applications running from within Messenger. In fact, this has already been done:
CookieRevised's reply to [request] LaTeX script
Other threads regarding LaTeX plugins:
New LaTeX Math Plugin
Math on MSN!
etc...
Other Examples:
How to embed images in a conversation window?
GREAT IDEA for a Plug-In... I want it sooo bad
Math in MSN (via LaTeX)
etc... etc...
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