Finding a small image in a bigger one

Question

Possible Duplicate:
Matching a rotated bitmap to a collage image

Given an image with a large dimension (> 1.000 x 1.000). What is a good approach to find a small image (e.g. 50 x 50) in the big one?

The smaller image can be rotated and differ in the size, but only with a 1:1 ratio.

It's not related to any programming language - I'm just interested in pattern recognition.

Thank you.

Answer 1

Look at my answer here:

http://stackoverflow.com/questions/2710799/matching-a-rotated-bitmap-to-a-collage-image/2710843#2710843

Answer 2

You might be able to do something with a log-polar transform as a pre-processing step on both images followed by cross correlation. The log-polar transform removes scaling and rotation variances, while cross correlation will identify translation. You might have to center the log-polar transform at various places in the larger image.