You need to install ZBar Bar Code Reader http://zbar.sourceforge.net/ and its headers before installing zbarlight.
On Debian
apt-get install libzbar0 libzbar-dev
pip install zbarlightOn Mac OS X
brew install zbar
export LDFLAGS="-L$(brew --prefix zbar)/lib"
export CFLAGS="-I$(brew --prefix zbar)/include"
pip install zbarlight