I’m not sure if this is a new feature, but I noticed that Google indexes images from PDF files. Google adds “[PDF]” next to the title of the page and offers a single option: “view PDF”, since it can’t link to an image from a PDF file.
Back in 2008, Google started to use OCR to index the full text of scanned PDF files. Now Google extracts images from PDF files and makes them searchable.
Here’s an example of query that returns many images from PDFs: [google pdf site:static.googleusercontent.com].