I have had the same question. I asked elsewhere and a user said, "It's as easy as copying the Zenimax folder and the ESO folder in My Documents." Sadly, that doesn't do anything for what we are asking about.
My specific question was:
"I cannot find information on this. It would be very helpful if we could do a backup. Especially, if we could transfer the image to another computer. Since account authorization and subscription is account locked, I don't think this is a way people could get the game for free. This feature is supported on the STEAM gaming platform."
I have ESO backed up on a separate hard drive.
I recently wiped the main drive and then instead of downloading the entire client I used the backup to make the download muchos faster.
First use their site to start a fresh download addressed to the correct place in your computer. When you have downloaded the launcher click install ( this will create the correct folders for you to copy paste the entire game client from your backup.) Now close the launcher.
There is a folder Entitled Zenimax Online ( the fresh install location of the file is in Program Files for 32 bit and Program Files x86 for 64 bit. The backup is wherever you made it ). This is the folder you need to copy, it contains the "Launcher", "The Elder Scrolls Online (EU or US)" and the "Uninstall" feature. Copy all three from your backup into the new folder ( your new folder may only have 1 file before you copy the new files but dont worry) ) and then re-open the launcher. Using the launcher just click repair and allow it to double check the game files.
The Whole ESO process took me less than 20 mins, I was upgrading my OS from a 32-bit to a 64 bit and the client still had no compatability issues. I hope this helps.
Edit - I used this process in Reverse to make my orrigonal backup. I just change the address of the client download when I did a "Fresh install" and copied the game files from my main install to the backup and then ran repair and checked it worked.
I think the Repair function probably registers the game's new location into your operating system.
There is a "Elder Scrolls Online" folder under the user's "My Documents" path. I think that is where some of the user and PC specific information is stored. I expect that gets rebuilt when you first run the Launcher and Repair on the new location. I wonder if that should be copied over, too.
easiest way to migrate the game is
1. copy the zenimax online folder over to your desired location
2. go to the account page and click download/install client
3. start the installation and be sure to select install DirectXand VC++
4. point the installation path (Browse) to the Folder you just copied over
5. the launcher will be installed, check the folder for Data integrity and patch or repair as needed
Done
Never argue with Idiots
They drag you down to their level and beat you with experience