Doubt about billing and transfers between regions of a Public AMI with public Snapshot

Let's suppose this scenario.

• AWS "User A" has created a public AMI based on a public Snapshot created also by "User A" at eu-west-1.
• AWS "User B" with a different account than "User A" copies this public AMI+Snapshot (because it is public) to a region at ap-northeast-1 in its own account.

After the process, "User A" still have its own AMI in region eu-west-1 and "User B" has its own copy of the "User A" AMI in ap-northeast-1 in its own account.

The doubt is, who pays the transfer of the copy?

• "User A", the originator of the AMI?
• "User B", the one who copies the AMI to its own account and region?

I hope I've explained my doubt correctly.

Best Regards, Carlos