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…
Cheers,
Frank Otto