You need to add the package when you are building the image in case you need more guidance in this I recommend you to see the Yocto reference manual http://www.yoctoproject.org/docs/1.5/ref-manual/ref-manual.html#ref-images . Another thing you could try is to download the module for python of the zbar https://pypi.python.org/pypi/zbar. I hope this works for you.
hi, thank you for the response. I have downloaded the python module but it requires zbar bar code reader from here and I think that there is no existing binaries for galileo architecture / yocto linux. I am not very sure how I can build this kind of image. any other resource or example i can use? Thanks for your help