I don't think the image file name matters squat for SEO and if anyone tells you otherwise they're spouting out more than they can possibly know since the search engines NEVER publish their ranking criteria.

Sometimes evidence is... well... the best evidence.

Seaching for "ball", the #1 hit has a file name called 751_multi.jpg. Too abstract? The number one hit for "Britney Spears" is an image named NUw8J0T5.jpg.

I know I hate more than anyone when someone posts a bad answer to my question, so officially my answer is "don't know"... but my advice, which you didn't ask for, is to not worry about it. SEO as a whole is strange in my opinion as Google has always done the same thing which is to ignore or even punish attempts to manipulate rankings in favor of delivering viewers the best CONTENT.