WordPress 3.5 introduced a new feature - when images are inserted into posts, the title attribute is not included in the image tag. This was done with the best of intentions relating to accessibility, as documented on Trac

Unfortunately, this causes problems for some Lightbox plugins, quite apart from stopping image tooltips from appearing.

This plugin hooks into the media_send_to_editor filter and inserts the image title into the html inserted into the post.

Does it do anything else?

No

Can it add a title to previously uploaded images?

Sadly not - that would require a different approach, involving edits to the database, which is well beyond the scope of this plugin.

Can you add a feature?

Errr, probably not. I put this together to fix a single specific issue. Updates are likely to be limited to making sure it continues to work with future versions of WordPress.

1.0

• Initial release

1.1

• Checks for existence of title attribute before adding anything. Filters title with esc_attr() to avoid any markup in the title breaking the img tag.

1.5

• Now adds titles to gallery thumbnails, which also works for at least some lightbox plugins. Thanks to photoMaldives for posting code and OC2PS for prompting me to update the plugin.

1. Upload the restore-image-title folder into the /wp-content/plugins/ directory
2. Activate the plugin through the 'Plugins' menu in WordPress