Short meta descriptions and google Webmaster Tools

In google Webmaster Tools, ( Diagnostics > HTML suggestions ), 41 pages are listed as having “short meta descriptions.”

These pages are all Media Library files which we’ve attached to a gallery page. The wordpress control panel Media Library gives you several options to fill out when editing a media file. These areas are “Title” “Alt Text” “Caption” and “Description”. However, the “Description” doesn’t seem to be a meta tag; it’s just where you can enter text to accompany the photo.

So, there is no obvious place to enter the “meta description.”

Any suggestions on how to handle this?

Is there an SEO plug-in which addresses this? We have All-in-One SEO, which works for pages, but doesn’t seem to handle media files.

Thanks.