Using CAPTCHA once was a good method to stop spam. Now that spam bots have gotten much more advanced some websites try to advance their CAPTCHA images to a point where they are unrecognizable.
Recently when trying to access a file on a popular file download site I came across this CAPTCHA:
Is it just me or do the cats look like dogs and the dogs look like cats? It took me 4 times to finally get the correct letter combination.