Hello! i've been making free book covers for people on nano and wattpad (my portfolio's [link]) and I used your stock here -> [link]
I know there are very few changes (oh, practically nothing, at all), but I hope the reason behind it is understandable. :/ as for commercial use - don't worry about it. I swear it's not - the author would tell me, if it were so, and I'd give them a link to contact you (or any other stock artist) for permission. Should such an event not arise, that would mean that it's purely for viewing pleasure.