The RevoStock Media Gallery plugin displays a gallery of media assets available for purchase from RevoStock.com.
The RevoStock Media Gallery plugin requires
A RevoStock user account (it's free!) - http://www.revostock.com/RegMember.html
API access - after logging in to RevoStock, visit: http://www.revostock.com/api.html
Currently, API authorization is only available to RevoStock Producers (users who sell content through RevoStock) but will be open to all members soon.
Also, you can earn more by joining "Share the Revo" http://www.revostock.com/Affiliate.html
Be sure that you've provided credentials on the Account page of the plugin's settings. You'll need both an email address and password registered at RevoStock.com as well as API authorization.