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Thu, 17 May 2007

Captcha problems.


For the last three days I tried different algos to solve this captcha:



As I described previously, first I tried to find number of crosses on the letter, but then found, that it is wrong approach, since frequently letter is crossed with small noise lines, so essentially number of crosses becomes completely unuseful information.
The last approach I decided to try is to present a letter as set of extrapolation functions, each one approximates points which are not placed closer than median error for previous functions. So it is somehow similar to how wavelet transformation works, where each new layer adds details to the picture.
But this approach fails miserably, the best thing I could get from it is to return that the closest to letter 'S' is '8', which is only remotely correct, but obviously wrong in general case.

So far I can not solve above captcha, but I have some additional idea, which is based on letter transformations I decribed previously. It will based on vector 'image' of the letter, i.e. I will create database of images created of lines only, each line will be a vectorized set of points, which can be moved. Searching algorithm will try to transform each database letter into requested one and check how many transformations required. It is possible that letter 'I' can be marked as similar to letter 'W' for example, since the latter can be created from the former using above transformations, but it will require more 'moves' than letter 'W' transformations.

This approach I believe is similar to how our brain works, and since there are no comments on my unified socket storage, I have some time to work with it.

For this topic I created captcha blog tag.

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