Google has also updated the image SEO best practices document to clarify that Google will parses img elements even when they're enclosed in other elements such as picture elements when indexing images.
Previously, the line read, "Google parses the HTML of your pages to index images, but doesn't index CSS images."
Now, the line reads, "Using semantic HTML markup helps crawlers find and process images. Google parses the HTML img elements (even when they're enclosed in other elements such as picture elements) in your pages to index images, but doesn't index CSS images."
Here is the before and after screenshots (before on right, after on left):
On another note, Google also updated the alt text and filenames in the examples to be more descriptive.
Forum discussion at Twitter.
