A Survey on Breaking Technique of Text-Based CAPTCHA

Table 4

Comparisons of typical methods based on nonsegmentation for breaking adherent CAPTCHA.

Example	Source	Success rate	Reference	Breaking method	Year
	EZ-Gimpy Gimpy	92%	[20]	Shape context matching algorithm	2003
		33%
	EZ-Gimpy	99%	[57]	Correlation algorithm	2004
	Program generation	55%	[62]	RNN	2011
	Program generation	54.9%	[63]	2D LSTM-RNN	2013
	reCAPTCHA	99.8%	[30]	DCNN	2013
	reCAPTCHA	31.75%	[64]	HMM	2015

Note. RNN: recurrent neural network, 2D LSTM: 2-dimensional long short-term memory, DCNN: spatial displacement of the neutral network, HMM: Hidden Markov model.