I just downloaded a few images and was surprised to see that they were .webp files, which some searching taught me is a Google web picture format. Although the Finder was able to thumbnail the images Preview did not open them. I downloaded the free XNConvert app from the Mac App Store and it did a perfect job of converting the images to jpeg. The UI design of the app is a little clunky, but it works great and is pretty powerful.
Thanks for sharing!!
I also found this app useful before, saved me some money as it did things that other apps charged for!