I enyoyed reading your article and bookmarked some links. But even using iStock for landing pages can get you in murky waters. Just ask twitter (they used a birdy from istock. After they became successful this was easily copied by copycats with almost the same url. The birdy can still be used today as it's royaltyfree). If you're going for stockart at least use it as a base for your design, not as the design.