Now, people using NextGen Gallery has an option to sell their picture through payment gateways (i.e. Paypal and Google Checkout).
To use this function you need to download the NextGen Buy Now plugin and activate it (you will need NextGen Gallery activated before hand).
Then you will see a “NextGEN Buy now” submenu under Gallery like this:
And you will see a “price” column added to the manage gallery page
and here is a front-end screen shot with Google Checkout:
A “Buy Now” Button will be added to a picture which has a price set in the manage gallery pages. Now it’s working with gallery view and single picture view.
Get it here
