I don't mean to sound hard nosed...and I have let people use my photos for paintings that weren't to be sold. But when I wanted ideas for paintings...I went out and bought a camera and a bunch of film...not only for ideas but if you are a painter and need slides for juried shows, a camera is indispensable (and learning how to take your own slides saves much money). It's how I got interested in Photography. Think any painter/illustrator etc. who works in a realist style(or even not) should learn how to take photos. Go around an art fair/show and take detailed pics of someones paintings and see the scowls on the artist's faces
In fact I've seen artists step right in front of someone with a camera. And yet it's OK for them, as professional artists, to paint from someone else's photograph? Obviously not a two way street there. Also I truly believe a painting should come from someplace or something you've felt or seen yourself, so using someone else's photo/image, at least to me isn't the best thing... Yeah it's nice to be able to paint from nature without a photo (hopefully from the painters own camera) for some guidance , but requires a lot of mosquito repellent in the summer and very thick gloves in the winter
...if someone is selling something derivative of your work, you oughtta get paid. It is strange that he asked you to send him the files.I too am amazed at how fast Google indexes stuff...it really is incredible sometimes.