How to develop a custom control for Infopath 2010 browser forms

I have a requ开发者_如何学编程irement to develop a custom control for use in InfoPath 2010 web browser forms, I've looked in all the usual sources (MSDN, InfoPathDevelopers Centre, SO etc.) but I haven't been able to find any reference or tutorials on how to do this.

Most of the documentation I have been able to find has been InfoPath 2007 specific and uses Active X for custom controls, a practice which is no longer supported.

In this particular case, the requirement is to add Captcha to whichever forms require it, but I'm expecting similar requests in the future.

Does anyone know of any resources for InfoPath 2010 custom control development, or even if this is supported?

Many thanks

Tim

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As far as I can make out this feature is no longer supported, it was previously possible using Active X (so not usable outside of IE) but now that support has been discontinued.