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".