Comment 7 for bug 480772

After so long, the most "correct fix" is in fact to add "-x c++" option to the gcc calling line.
Another related problem is due to the different packages that represent opencv in the new version.
In Karmic, depending on "libcv-dev" would get you all the necessary packages; in lucid, these packages are unlinked; libhighgui-dev wont bring libcvaux-dev on its dependencies and neither will the opposite. The fix is to add:
"libcvaux-dev, libhighgui-dev, libcv-dev" to debian/control instead (the third is not necessary but IT FEELS RIGHT to do this right now so it won't break again in the future.

As for the software itself, the new release (harpia 1.1) just changes the header files and the "-x c++" thing, this release can be downloaded from http://www.das.ufsc.br/~scotti/harpia/harpia_1.1.tar.gz (the only changed file is gerador.py and it does fixes the opencv2 issues)
This elegant fix comes from Michal Krombholz.

I'll try to pass it to my ppa as a appropriate .deb and then submit it as SRU (https://wiki.ubuntu.com/StableReleaseUpdates) later on.