(Cross posted from Random Acts of Photography where you can read the entire post and its updates)
WordPress.com introduced the Gallery feature back in April 2008. However, a full Gallery-specific WordPress.com Support document appeared only in September 2009. My Not-the-Official-WordPress.com Gallery FAQ was an early attempt to bridge the information gap and is still being updated over various changes and upgrades to image handling and the Gallery feature on the WordPress.com site.
A Small but Important Disclaimer: Since their introduction, the Gallery feature and image handling behavior on WordPress.com have been a continual “work-in-progress” and things may go pear-shaped without warning. The Gallery behavior on WordPress.com blogs as described below is correct as of this Post’s latest update and was tested both pre- and post-publishing on my WordPress.com blogs. Updates will be listed here, as well as current problems which will be removed when solved.
What is a Gallery?
A Gallery is a thumbnail set of images that appears in your blog Post or Page. Clicking on a thumbnail image will open either the original image or a larger image in a separate Attachment page.