Aaron Bradley posted on Google+ that Google has changed the article schema requirements documentation specifically for AMP pages that you now need to provide higher resolution graphics in that AMP markup.
The image requirement went from 696 pixels wide and 300,000 pixels in total, now up to 1,200 pixels wide and 800,000 pixels in total. Which means if you have been showing 696 pixels wide images in your schema now you need to go back and change the process to show images that are 1,200 pixels wide.
As I documented at Search Engine Land, here are the before and after screen shots of the change in the developer docs:
Paul Shaprio posted on Twitter that “this is the non-sense that makes people hate AMP and Google.”
Forum discussion at Google+.