http://pwndizzle.blogspot.com/2014/07/b ... ptcha.html

IM using this command but not work accurate
convert fbcap546.jpg -colorspace Gray -gaussian-blur 9.0 -level 0,25%,0,1 -depth 1 -paint 0.01 test.png
how I could use a method similar to this post
http://pwndizzle.blogspot.com/2014/07/b ... ptcha.html