A query question that came up in a recent conversation: I write historical fiction loosely based on my family's history. In my research, I found several authentic artifacts that I've worked into the narrative, and there are others, that could be borrowed, to help illustrate key elements of the story.
Examples include a copy of a handwritten resume that my grandfather prepared in 1919 as he got ready to return to Trieste after WWI. There's a photo of my great-grandmother's house just after it was destroyed by an Allied aerial bombardment; dust hangs in the air, and her body has not yet been recovered.
(1) Could I use these in the novel?
(2) Would they make the book more appealing?
(3)Would it be appropriate to mention these in a query?
(1) If use as illustrations, no.
This is supplemental material that is useful for your website, but not your query or your manuscript. Right now your manuscript has to do the work. If an agent is interested, and signs you up, of course you'll tell her about these items and see if it fits into her submission strategy.
I will tell you I've never offered illustrations or supplemental matter as part of an adult novel. Middle grade and YA, sure. Non-fiction, of course. Not novels.
To use one of my client's as an example: when Gary Corby sent me his manuscript for what became The Pericles Commission, it didn't have anything extra. The books now have maps, and an author's note, and a historical timeline. All those are wonderful for the reader, but the manuscript was what got me and it's what sold the editor.