Gmail – Easiest way to move Google Photos from one account to another

The procedure you referenced in your question only forwards new messages you are looking for a procedure that will also bring over the oold messages: The are several questions/answers on the gmail help forum.

here is one:How do I transfer all of my emails from one gmail account to another?

the summary of the procedure is :

1) Enable POP on the old account and select for all messages. 2) In the new account in settings/Accounts and import "Add a POP3 mail account you own" 3) A key piece of information is how to log into the account:

POP Server: pop.gmail.com
Port: 995
Uncheck: Leave a copy of retrieved message on the server.
Check: Always use a secure connection (SSL) when retrieving mail.
Uncheck/Check:Label incoming messages – Check it if you want to Label the messages.
Uncheck/Check: Archive incoming messages – Check it if you want to archive > messages instead of sending them to the Inbox.

Albums in Google Photos are completely separate from folders in Google Drive. Thus, you will have to export the photos from Google Photos, and upload them to Google Drive. I'm going to assume you use Backup and Sync to sync your Google Drive with your computer, as that will make this process easier.

You can download the album from Google Photos, and save it in a folder in your Google Drive where you keep your photographs. Then, unzip the folder you downloaded, and add your photos to the shared folder. If you don't use Backup and Sync, the only difference is that uploading the photos to Google Drive is done through the web app (drive.google.com).

I'm sorry that the migration is not done through the cloud. Migration in the opposite direction is supported—you can copy images from Google Drive to Google Photos (syncing was disabled in July 2019). But, photographs were intended to be used in Google Photos—that is why Google doesn't really support migrating the photographs back into Google Drive.