training SIFT features in OpenCV

Question

I have created a small SIFT application that grabs the keypoints and saves it out to a text file. I am using this to grab information from a logo (say AT&T) and use that

Answer 1

A simple starting point would be to collect SIFT/SURF descriptors of several AT&T logos, and use FLANN on them. Then, take a test image, compute the descriptors and do a range search and determine the nearest-neighbor distance, etc. and try to figure out a metric of "closeness".

Answer 2

You can use PCA to reduce number of dimensions and then you can train some kind of classifier like SVM on set of vector features extracted from logos. also you can use BoW (bag of words\features). also you can google on "logo recognition" a lot of material availible.