Well, presumably, something could be hacked together in order to do that by means of gstreamer and python.

gstreamer deploys a plugin that overlays any text over a video source:

http://gstreamer.freedesktop.org/dat...xtoverlay.html

by means of a gstream pipeline more or less like the following:

v4l2src ! textoverlay text="Test" valign=top halign=left

I even tried to use that pipeline as the default video source by messing in my gconf gstreamer setting, hoping that the default camera app would pick it and use it, doing the following in the xterm:

gconftool-2 -s /system/gstreamer/0.10/default/videosrc --type string 'v4l2src ! textoverlay text="test" valign=top halign=left'

but it didn't work. This could mean the the camera app does not use this gconf setting, but a hardcoded pipeline. I should inspect the source code.