DeBoer letter of copyright infringement

[TerriDe]

Good Morning,
I used to run a small graphics service, myself and an occasional intern.  I received email notice from a company I used to create newsletters for, that the owner had received notification from DeBoer of copyright infringement, and demanding payment of $1,700 for 5 years of use of an image.  It was located in an old issue of their yearly inter-corporate newsletter (2008).  I let them know that I always used "free to use and share" licensing search and my intern was instructed to do so, but cannot guarantee the source of an old image like that, and to take it down.  In fact, I suggested that "old news"... should all be removed.  Good Lord, I see that they have newsletters going back to 2005 online!  My understanding at the time of the work was that these were dated materials, inter-corporate, never intended for "long-term use."  Any images I would have purchased would not have contained "long-term use" licensing.  My question is, since I had no contract with them, will I be held accountable for this or other images that trolls locate?  I no longer maintain that sole proprietor business, but how can I help this old client?  I believe in good business.  I thought maybe I could go back to all these old newsletters and remove images if they feel for some reason that they want to keep them online, or does this just implicate me.  I hate this litigious society we live in...