Counting vechicles in an image I have been trying to implement an algorithm for successfully counting cars in an image. I have tried implementing A Method for Vehicle Count in the Presence of
Multiple-Vehicle Occlusions in Traffic Images

It estimates the background from a set of various images. I have looked into various other techniques for this purpose and all of these in one way or the other use either background estimation from a set of images or require a video. I have as an input, traffic images where the background (probably road in most of the papers) is hardly visible. Moreover, the images are from different areas so they don't have common backgrounds as well. How should I proceed in that case ? 

I am thinking that if somehow I can match the structure of vehicles (car) then probably they can be matched. But I don't know if this is feasible and if it is how to proceed since the image contains multiple occluded vehicles as well.

Any hints or even research papers are also welcome.

A sample image is as follows:
As mentioned the object counting problem is very challenging. A good account of some common approaches is given in http://www.robots.ox.ac.uk/~vilem/NIPS2010.pdf. 

Creating a SIFT feature database on training images would appear to be the natural path to go down. That in combination with some image segmentation may be the way to go.

Another path might be to look at HOG http://chrisjmccormick.wordpress.com/2013/05/09/hog-person-detector-tutorial/, which is similarly a feature detection algorithm, could be adapted for cars.