If you have a Moto G4 with the model number XT1624, a factory image is now available for download from the Motorola website. At this time this is the only factory image available to download and flash to a device, and there's unfortunately no information on when or if factory images for other devices will be relisted. Having said that, it's also worth mentioning that you may not have need of the factory image, but if you like to tinker with your devices and you want to be prepared if something goes wrong, the factory image can help as it'll allow you to flash back to stock software.
If you want to keep the factory image on hand should you end up needing it, flashing it will require an unlocked bootloader, which is something the Amazon Prime exclusive model of the Moto G4 does not have. Having said that, this device has model XT1625, so the factory image wouldn't work for the Amazon Prime exclusive model anyway. Nevertheless, it's a good idea to know up front just in case you weren't sure. On the Motorola website where you can download the factory images, you'll be prompted to sign into the site before you can download anything, and you can do this with a Motorola account but you can also sign in with Google if you prefer.
Once this is done, you'll end up needing to accept some terms and conditions, and just below the acceptance box you need to check there will be a drop down box you can click on. Here you'll find the product families which you're looking to download software for, which as stated is only listing the Moto G4 at this time. It's possible that the Moto G4 is the only product family that can be selected due to the website using a new direct download system for factory images, and if that's the case then other devices may show up at some point. Lenovo nor the Moto team have confirmed any details regarding the lack of factory images for other product families, but it seems unlikely that they would leave consumers without a way to get factory images for older devices for long.