I suspect that most of the "known" Maine 2 footer photos have been copied, re-copied, scanned, pirated, and stolen, and that it would be nearly impossible to prosecute anyone for using one. When I was the curator of the Walker Transportation Collection at Beverly Historical Society from 1969 to 2008, I had over 500,000 prints, negatives, slides, etc. under my thumb. I would guess that 90% of them were also available from other sources, as railfans were notorious for copying. Even the infamous rubber stamp warnings on the back of prints didn't deter folks from copying. Hell, L. B. Walker himself copied every image that ever crossed his desk from the 1930s until the day he died in 1969, and he was proud of it. His reasoning was that copying and distributing (at no charge) prints of every form of New England transportation only served to get more people interested in the subject. He DID usually credit original photographers if known. Some folks got really upset by that practice, but L.B. referred to them as "hoarders" who wanted everything for themselves. He believed in "spreading the wealth around."
Today, with so many ways to copy images and distribute them (Walker would have been in 7th heaven if he had a scanner and a computer), there's virtually no limit to what can be procured. I saw a brief video clip on YouTube the other day of the B&M Talgo Train in action. It was copied from an 8mm movie, which the B&MRRHS issued on VHS tapes years ago. Now someone grabbed it from a deceased fan's collection and is putting all his stuff on YouTube. Guess who took the Talgo Train footage? Right. . . ME. Is my name credited? No. Do I care? No. If people are happy to see the Talgo in action going through North Beverly in 1962, great! Isn't that what it finally comes down to?
Onward and upward.