Regardless of the delivery method - online, off-air, newspaper/print, etc., if you didn't create the image, you don't have any right to use it other than to view it for your personal enjoyment.
Public domain only occurs if 1: you give up the rights to your works and specifically grant unfettered use to the work; or, 2: The work has lasted the life of the creator PLUS 75 years and has not been reassigned.
A work published is just that - published.
An alternative would be to buy a royalty-free set of the same type of images - there out there and will save you problems in the long run.
Of course, you could alweays use them and take your chances...not smart given the current trend toward pursuing copyright cases...but...
Just to clarify, it's 75 years for domestic distribution only.
Wait until you deal with stuff that is for international distribution for broadcast and home video distribution like I have to, then you will learn about the evil lawmakers in France, the U.K. and Germany where titles that are over 100 years (Trip to the Moon) old are still under copyright, it's a nightmare.
Public domain is only public domain where you can prove it also. We work with all of the studios and they want a Thompson & Thompson or other reputable published source to verify PD, even if you get all rights cleared and PD from the Library of Congress/National Archives. There is common sense, then there are studio lawyers. Neither shall the twain meet.
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