If I were going to draw sprites ANYWAY, yes, then I'd let you use them, and in fact be happy the stuff I spent time on got to more good use! I don't do any sprites however, but the kinds of art I DO make, I am glad to share if someone need it!
The only reason I can think of for doing otherwise is spite. Spite is a Bad Thing.
Not wanting someone else to capitalise and leech off your hard work without accreditation, recognition, or legal recompense if they were to make a profit off it is
spite? Armok you are honestly getting worse at this whole 'being a reasonable human being' thing.
This is not about what you'd do in this situation. This guy wants to protect his artwork, for entirely valid reasons, and here you are being all "Well for superior sharing caring human beings SUCH AS MYSELF these petty concerns are trivial :smug: "
But being on-topic, yeah, obscurity as security is a policy that's always going to eventually fail, especially since no matter what you do, any screen-capturing software can easily circumvent it. Just license your work, make sure people can tie the original source back to you some way, and that's pretty much all you can do without going to some insane and pointless lengths.