Selected answers from the Dumb SEO Questions G+ community.
Alan Bleiweiss: As long as image name and alt attribute are properly optimized, title is irrelevant or can go too far regarding SEO.
Check with WCAG 2.0 guidelines though regarding accessibility standards, where that field may be required for that specifically. I can`t recall off the top of my head.
Casey Markee: Actually, the "Title Attribute" is used by Pinterest. As a blogger with a lot or visual rich media, this would allow you to optimize for both Pinterest and Google Images.
Title Attribute = Pinterest
ALT Attribute = Google Images
So definitely something to keep in mind if you for example have any desire to make your image content "pinnable."
Bill Slawski: I took over an SEO campaign for a large, well-known university in Maryland, and the SEO who was leaving had told their marketing manager that the title attribute could be used with most HTML elements. (Which is true except for base, head, html, meta, param, script, style, and title) Their marketing manager spammed that HTML by adding title atttributes almost everywhere with the keywords they wanted to rank for.
I took a look, and called her right away to suggest that using titles like that wasn`t necessarilty a good idea. I am happy that a search engine didn`t see it.
A title attriobute is intended to provide tool tip information, such as a "click to enlarge" so it doesn`t describe things like alt text does, but it does appear on hover using some browsers.