Correct me if I'm wrong but AFAIK it just works using a hash of the image so any small change to an imagine would make reverse search fail.
Discussion
Sorry to say that but you're wrong. Search engines offer reverse image search using visual patterns, not hashes.
Good to know
Pretty sure algorithms exist to requantize the image and ignore hash alterations, similar to the way Shazam, MusicBrainz
[reposting without paste-failure] Pretty sure algorithms exist to requantize the image and ignore hash alterations, similar to the way Shazam, MusicBrainz, and SoundHound work for audio tracks.