Fellow Mac users, I've been approached by an organization that wants to use five digital photos I shot for a photo wall in a multi-year exhibition. The pictures are available at a resolution of 1600x1200 pixels. They want the copyright for that purpose. I am willing to grant them the copyright for the purposes of that exhibition and told them I'll still need to get the permission from the people displayed on the photos. But I'm really stumped regarding the price: How much I should charge them? I don't have any experience with selling photos, so I'm thankful for any advice.