I had intended the function to be optional. I'm not a big fan of programs coming back to bite their users, even if their users might be evil. However, you are right that some spammers would forget not to include the text and thus their graphics would be more decodable. (Obviously images not intended for decoding like captchas would not have these tags.) I don't see this feature biting most users, however, other than perhaps if they don't want search engines to know what text is in their images. In theory the text would not reveal anything a human could not learn by just looking at the image, so it's not secret, but in practice certain types of very tiny or highly distorted text might be revealed which would not be visible to a human. Clever software could detect that but I think that's overkill.