Some sage advice from everyone and I thank you for your input.
Firstly, this is not something that I expect WILL sell squillions, but as has been said, IF I don't ask, then I don't get and formalising some sort of agreement and payment up front makes it easier later if demand increases.
One important point is this, my friend is an old work colleague and it was actually his idea to ask me for the use of one of my photos for his product and offered image author credit on his work. I then asked if he meant credit as in a fee to use and he said that he would be happy to pay for it as he appreciates the time and effort and money that goes into the astrophotography investment most of us have.
So, we discussed, quite openly, that neither of us really had any idea of how much to charge or offer for, lets be honest, a REASONABLE astro pic i took of The Sombero Galaxy which he liked......yes, there are MUCH better ones out there, but it was nice he asked me specifically for the use of mine, rather than just rip it off without my knowledge or simply buy a stock version elsewhere, which I am sure he could do without much trouble.
Apart from the childhood fantasy of having a pic of yours shown on an international product website and somehow, by the inclusion of my pic, his product gets more notice and he sells more product, to the point of making him money, then yes, I would quite like this scenario, BUT I don't know how charitable I would feel if he got rich off it and I was left holding my "warm and fuzzy" feelings while he lived the high life as a result.
I am not saying my humble photo would be the catalyst to his outstanding success, because ultimately it is simply window dressing on his product, which HE has created himself, so therefore, my contribution is minor in the overall scheme of things.
Anyway, I have offered him the USE of the pic for a fee, with the understanding that the image credit bears my name and copyright 2014 in all reproductions of his work.
Based on the yet to be established professional astrophotography reputation of mine
, I think anything reasonable is better than nothing. I am yet to have a response to my offer, but if nothing comes of it, or conversely, his works sell their pants off, then at least it is a start. I don't have the time or the inclination right now to formalise a business or contractual paperwork to pursue this formally in order to protect my image rights or enforce profit sharing or fees for use other than this simple agreement for now.
So, at this stage, I will see what he says to my offer and see what happens next. I like Al's and Doppler's ideas of a percentage cut of the profits or sales, I just don't know how possible it would be to track this, as the product is being sold online and I have no real visibility on the numbers sold etc....but I will mention it to him if he baulks at paying the fee or goes cold on the idea. As I said, he is a casual previous work friend with whom I infrequently chat to online, so it's not a biggie if it all goes south somehow, it is not my primary source of income but would be nice to have some gravy in order to complement my growing astro equipment collection
Thanks again for everyone's input and to H for looking out for me the way you have, I sort of knew you would chime in on this topic the way you did, good to see the fire there is still burning strong
Cheers
Chris