Tineye doesn't search the entire internet, just a group of sites on its index. As a result, if a search turns up multiple other locations, it usually means it's a fake; however, if a search turns up 0 results it does not mean a picture is an 'original'. It only means that the picture has not been duplicated in the places tineye looks.

If it was 100% accurate, a tineye seach of redgoat's avatar would turn up Darrah's myspace page.

It's a very popular tool for people checking to see if Craigslist escort pics are real or not.

test case:

CL ad



tineye search:

http://tineye.com/search/4010e061c056f6da79c5010af602bfc57422f2ab