I agree with bgar3 and D. Bergin. Back in the day, photos were usually printed in their own section in the middle of books, on better paper, and the pages were sometimes referred to as "plates."
I am not an expert but I know enough to categorically say that what you have are not printing plates.
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The GIF of me making the gesture seen 'round the world has been viewed over 425 million times! 
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