overlay a text or a graphics from saMmapLoopback

Hi,

I am working on omap3530.

I am currently working on Armstrong OS (kernel 2.6.32) which has in-
built command of "saMmapLoopback" which gives the loopback of the
camera. In my application i want to overlay a text or a graphics on
that loopback image via sending some command from RS232.

How do i go about this application?

Kindly Oblige.