To try this feature, open a Google Doc and choose Insert > Image. Once there, you'll have a number of options including uploading an image, pasting an image URL, or searching. Choose Search and you'll notice that there's a line of text below the search box that reads, "Results shown are labeled for commercial reuse with modification." (If you'd like to know more about the finer details, you can read the longer version of the explanation.)
To make it even easier, the search results show an image preview and you can quickly scroll through pages of results. You can also use colour or image type to further filter the results. This is super handy if you're looking not just for a type of image, but also one that matches your aesthetic.
BTW -- I discovered this feature by watching the Google for Work App Show, so I'll give them a shout out.