section_heading: Image-recognition CAPTCHAs
paragraph_text: Some researchers promote image recognition CAPTCHAs as a possible alternative for text-based CAPTCHAs. To date, only rapidshare made use of an image based CAPTCHA. Many amateur users of the phpBB forum software (which has suffered greatly from spam) have implemented an open source image recognition CAPTCHA system in the form of an addon called KittenAuth which in its default form presents a question requiring the user to select a stated type of animal from an array of thumbnail images of assorted animals. The images (and the challenge questions) can be customized, for example to present questions and images which would be easily answered by the forum's target userbase. Furthermore, for a time, RapidShare free users had to get past a CAPTCHA where you had to only enter letters attached to a cat, while others were attached to dogs.<ref> This was later removed because users had trouble entering the correct letters.