Ну что же, я оказался прав. Мне ответила тех поддержка Бигстока, где собственно эти ребята и хотели подключить API. Только расширенная лицензия.
Grete:
Hello
In order to offer images on merchandise, an Extended License is needed. This license is a separate purchase and is not included in our monthly subscription plans.
Image's can either be downloaded with Extended Licenses by purchasing credits, or by participating in our api partnership.
Unfortunately, we do not support this program from the Live Chat, but our API team will be glad to assist you. You can address your questions to
api@bigstock.com to reach the team directly.
I have also included the link to our API partnership information: bigstockphoto.com/partners/