Captcha is used for validation.
Simple example,when you book a ticket frim irctc at last after filling name,age and etc.You get a image with some text in it and you have to write same text in the text box.
That is captch.
Hey normally captcha is disabled on test environments!! The captcha image has some text, so on spying u would not be able to get that value, better would be have a msgbox and type in manually. What properties are u able to view for the capture image, are u able to get the alt property of the image. If yes then capture the same and enter that in the desired text box/editbox
Depends on the conditions of your test and how your particular captcha works. Most captcha pull random words from a table/dictionary. If you are not specifically testing the captcha and don't need to test the 'see' of the word in the image, you - or someone - can set the word in the captcha dictionary / table to only one word and you can hard code the word in your script - if you are testing the captcha - there are ways to de-construct the image at the pixel level and reconstruct the word - but that is not a 100 precent accurate procedure and to be honest - most tests are not a test of the captcha but a test that the logon using a captcha works - so putting one word in the table - dictionary is acceptable.