You do know that anyone can make your own stamp from any photo you want usps.com
With the condition that you own the copyright on the content, and the content is acceptable by the USPS. It is their sole decision whether they agree or not to allow your "picture" as legal postage based on their criteria and discretion. In our case, we got that approval.
So it's not really "anyone" or "any photo" as you claim. As in any case, the fine print does matter.