This extension attempts to make Google Images look and feel like it did before they changed everything on August 6th, 2019.
Note: in mid-2022, Google got rid of the normal "search by image" results and replaced it with "Google Lens" results. If you want to revert it back to how it used to be, please use the extension Disable Google Lens as well.
This extension is available on Chrome Web Store.
It is also available as a Firefox Add-On.