The canonical repository is the WHATWG HTML repository.
This repository contains the history for a subset of the HTML Standard
covering most of the Embedded content section,
including the picture, source and img elements.
The history of earlier proposals for the picture element, before it was adopted in the HTML specification, is also in this repository.
If you found a problem with the document, no matter how small, please file an issue in whatwg/html.
Old issues can be found in this repo as well as in W3C Bugzilla.
Join the RI Community Group and help us make the Web a better place ... for images :)