In the past few days, I have been adding my newspaper articles from Newspapers.com and other sources to Zotero. I don't use Zotero to formate my citations. Instead, I use it to make sure I have all the information I need to write my own citation.
When downloading the images and labeling them I would use the "page number" provided by Newspapers.com. Later I discovered that the "page number" is not really the page number in the paper but rather an image number.
I have considered two ways of crafting a citation from this. One would be to use the actual page number with a p. to signify it is the actual page number or to use "image" instead of "page".
"Bridge Winners" The Press Democrat (Santa Rosa, California), 14 October 1956, image 20, cols. 4-5; digital image (http://www. newspapers.com : accessed 27 May 2020).
The second would be to write a "print edition" style newspaper citation and add the image number in the second layer.
"Bridge Winners," The Press Democrat (Santa Rosa, California), 14 October 1956, p. 6B, cols. 4-5; digital image, (http://www. newspapers.com : accessed 27 May 2020), image 20.
If the first option is used I think it should have the addition of "citing page 6B" (without the quotes). This would allow a user to locate the page on a roll of microfilm or another source.
I think both formats would work but wanted to make sure I didn't forget something,