Having both title and alt on an image is redundant and can hurt SEO, so title was retired. The current cascade is to ignore title and to use alt. If alt is empty then caption is used. If both alt and caption are empty then title is used as the fallback. http://en.forums.wordpress.com/topic/new-media-upgrade-has-major-flaws-wordpress-support-please?replies=26#post-1081464
more here:
http://en.forums.wordpress.com/topic/new-media-upgrade-has-major-flaws-wordpress-support-please?replies=26#post-1081764

Accessibility
It's important to understand this from accessibility perspective. Alternate text (ALT) attribute is important in situations when an image cannot be loaded and also assists visually impaired people who use apps to read ALT attribute, so what’s in a picture is known.
http://onecoolsitebloggingtips.com/2012/01/08/get-the-most-out-of-image-search/

It's probably good practice to add a title tag in too though - I read somewhere that if you have a link on your image you should use the title tag to describe where you image links through to.

Sorry I can't be more specific. If in doubt its probably best to use both, but just word them slightly differently

Hope that helps! :)

It's probably good practice to add a title tag in too though - I read somewhere that if you have a link on your image you should use the title tag to describe where you image links through to.

Sorry I can't be more specific. If in doubt its probably best to use both, but just word them slightly differently

Hope that helps! :)