Ask when you can, I think that is what most want, the respect of knowing you acknowledge them for their hard work and you will not just forget them once you do happen to maybe make something using their work. I am sure there are exceptions, but most art people are not so unreasonable as to not be at least reasonable ;-) (problem is that it DOES take time, no offense to you mason, I am merely stating a fact I myself had to endure. Yes, many times it is hard to realize WHO did what, but it's worth it at the end when you find our how polite folks are when contacted politely and respectfully for their good work....be great if it were easier but good things take time I guess, I think sometimes it takes LONGER to do all the asking and contacting than any one, or two, or MANY pictures....in fact I'm certain!) Take care.