Learn to read

[2] ICDAR: http://dag.cvc.uab.es/icdar2013competition/

[3] Naptha: http://projectnaptha.com/

[4] http://googleonlinesecurity.blogspot.com.es/2014/04/street-view-and-recaptcha-technology.html

[5] MAVEN: http://www.maven-project.eu/index.html