obvious approach for corporations is to simplify the math.
the model is made from X images, from Y artists, each artist has a percent contribution to the total. between 0 and 100 percent.
so each time money is generated by the model, the contributors get their share.
as a bonus, it is easy to understand how that share was derived. so it is implicitly fair.
(please keep in mind that this “artist’s share” will be a percentage of the net revenue generated, and that this percentage will probably be a trade secret or some such.)
(any works from artists unable to be paid, meaning public domain or otherwise, will be handled by the corporation for the continuous and never-ending improvement of the platform that makes it all possible.)