There is a small link in the footer of all search result pages on Google to give Google your feedback about the results on that page. In the past, it was just a way for Google to obtain your query, browser information and a message from you about the query. Now, Google lets you submit and highlight a screenshot of the actual search results page that you are looking at.

Here is a screenshot of the feedback form with screenshot capabilities (might be the first time I took a screenshot of a screenshot):

The form from a few years ago looked like this:

Nice find @glenngabe!

Forum discussion at Twitter.