Many people have already mentioned how great the reverse image search is, but I want to point out that this extension also has a very powerful "OPEN IMAGE" option. Open Image, lets one see and save images that don't have IMG URLs.

For example, sites like artsandculture.google.com will send very high resolution images as tiled PNGs and use JavaScript to stitch them together. Each tile is just a data blob so all the other extensions I tried (Download All Images, Save Images, etc) failed to even detect that the image exists, much less let me save it.

I don't know how Search by Image is able to find images that other extensions miss, but I hope that eventually the author (Armin Sebastian @dessant) will create an extension that can download all such images from a page in a single click.