Hi Dan, Please no apology neccessary. There is a lot of free clip art (Royalty Free Clip Art ) Available. Thankyou for the link... and it does state free on the site. If I use any I will mark it as free domain. The ony thing you do not know is who put it there and where it came from originally. It is always best to cover yourself.
As you know many places will not allow you to post anything if it has no credits to protect their places.
Hugs Maureen