This plugin is supported by the current release but needs some fixes

The Captcha Image Plugin allows you to use Captcha images for comments and user registration, as a measure against automatic spam attacks.

CFlash is very easy to use

This plugin is no longer necessary for most users because similar functionality has been integrated into b2evolution's core.

This functionality is now built into b2evolution v5. See Colorbox.

The Disqus plugin allows you to use comments from the social commenting website Disqus. The plugin inserts some javascript that will display the number of comments on a particular blog post when viewing a blog and a comment entry form when viewing a particular blog post. Comments can be enabled and disabled on a per comment basis. Find out more about what Disqus does here. You can check out a blog post to get an idea of what Disqus can do here.

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This plugin allows integrating Flickr images into your blog.