Letter Derotation
I’m getting kind of done with captchas but here goes another post on them. You may have read Slightly Shady SEO about how to derotate letters. Here’s my easier technique. Add up all the black in the vertical lines of the letter, find the average and then check for spikes above that average. These spikes are probably vertical lines in the letter like the back of a ‘d’ or a ‘p’ etc. Then we simply rotate it around by a few degrees until we find the rotation with the largest vertical spike above the average. We then need some extra checks for symettry and so on but that’s the basics.
Saturday, April 5th, 2008
