Your account rank doesn't matter but newbie is being prohibited to post image. You shall have bought copper member first in order to allow you to post picture or image related to your bounty campaign. You don't need to be a bounty manager for that.
Can I still buy a copper membership?
Didn't see an option.
Yes, you can.
Try opening this link:
https://bitcointalk.org/index.php?action=credit;promote.
It will link you to the page where you may purchase copper membership. Because of the price of bitcoin, it could cost you roughly $27/0.00041091 BTC.
There is another option for you to publish an image without having to pay for a copper membership. You can try to earn some merit so that your account will be able to publish images.