I think you may find this post interesting - http://www.searchenginejournal.com/image-alt-text-vs-image-title-whats-the-difference/
Note the following:
"Include your main keywords in both, but change them up. Keyword stuffing in alt text and title is still keyword stuffing, so keep them relevant and meaningful"
If possible I would populate both title and alt tags for images but make them different variations rather than having them as the same. I know this is a challenge and as Dirk mentioned as you may be limited go for identical but try and be as relevant as possible. Depending how your site is setup you could potentially custom code your template to populate the two elements from slightly different but relevant data on the page.
Again I think you might find this on-page SEO post by Rand interesting -
"For search engines, the image's title, filename, surrounding text, and alt attribute all matter from a ranking perspective. In particular, those doing SEO should know that when an image is linked, the alt attribute is treated similarly to anchor text in a text link."
http://moz.com/blog/visual-guide-to-keyword-targeting-onpage-optimization