I don't keep a database, however, I do go through great pains to credit the artists (not out of legality, but out of appreciation), sometimes to the point of lunacy in large complicated scenes. Sometimes in large scenes it might be easier to say what is yours, rather than what isn't.

When I install an item (which I only do usually if I plan to use that item in the current render) and I check then for the readme to see who did it for the credits. Since I usually export from Poser a good majority of the items I use, that also makes it easier to keep track of who made what. When I put up the picture, I list all the items and if I use one of those items in the future, I reference the credits from the previous image. Course if there is no readme on something downloaded long ago, then I usually just say 'item by ????' to signify that it was someone else's but I don't know who, or I'll list the site it came from if I remember (like item from 3Dcafe). So far this system has worked well for me. I do try to credit free stuff and marketplace items, but will usually just say 'All the rest from the Vue Library' rather than listing out who made what tree or texture (unless they were specifically downloaded separate from the e-on CD's)...

ShadowWind