captcha is basically to stop spam. its quite an efficient way and is now being used in numerous websites. its got different forms such as adding, subtracting (basic mathematical calculations) and normally presenting the letters that the captcha displays. but the most annoying thing is sometimes its hard to read the label and one can end up typing in different letters and different numbers thereby causing a misunderstanding. this happens usually when the words are clustered or when its hard to tell the difference of whether its a lowercase or an uppercase letter. on the whole its for protection process and is widely used only because of its efficient "protection regime".
