Discriminatively Trained Deformable Part Models
Why not start with some easy-to-understand MATLAB code so you can starting advancing your research this year, not this decade!?! Also, if you are able to build on this work, you will have an easy time publishing object detection papers that will actually be treated seriously by contemporary vision researchers. So my advice is to get voc-release-3.1, and read the following PAMI paper.
P. Felzenszwalb, R. Girshick, D. McAllester, D. Ramanan
Object Detection with Discriminatively Trained Part Based Models
IEEE Transactions on Pattern Analysis and Machine Intelligence, Vol. 32, No. 9, September 2010
pdf Source code
Be warned that pff is probably smarter than you so you will not be able to understand 100% of everything he says, but because it is well-written code you will not have to understand all of it. If you want to be a Vision Jedi, look at the code, read the paper, discard the downloaded code, and write it yourself.