Also use of the image needs to be considered. If the photo is going to be the mascotte. Price for rent of a photo for one year is around 300 euros, depending on use could be more. At least thats what I would ask. How long is he going to use the photo? There is your answer. If he want a lifetime exclusivity, you can ask 10.000 euros, maybe even more. Its not as simple or factual as I explained, but thats how you need to think. Forget stock pricing, this is hard cash.