Where can I find the source of the image?
You can click the tag name to go to the source on GitHub for that particular tag. Every tag has its own branch.
master branch is used as a landing page and to store some statistics used by this page to populate the table.
Temporary tags/branches might not show up in the table, but are also generally not for end-user consumption.
Clicking the commit sha brings you to the exact source of that commit.