Check out the Ephemera Assemblyman blog. If you look at the right column and scroll down, you will see one heading labeled “resources”, and another labeled “images.” Each link points to even more vintage images. I’ve been looking at them for hours, and still have barely cracked the surface. Have fun!
Flickr is an incredible source for scans of ephemera from all eras. There is so much to find on there. One of my dreams is to somehow organize and catalog all of this; until then, all I can give you is a somewhat ordered list of things I’ve found. Remember that this only represents a sliver of a portion of what’s available on the internet.
As a props person, you’re always looking online for images, whether as research for pieces, inspiration for set dressing, or as elements for a paper prop.
The New York Public Library has a great digitized collection of images in their Digital Gallery. Some proptacular highlights include cigarette cards from pre-1900s to the mid-20th century; dust jackets from American and European books, 1926-1947; decoration in the Age of Napoleon; and a collection of restaurant menus from 1851 to 1930.
There is also a ton of theatre-related photographs and ephemera, such as the Vandamm Studio Photographs of theatre productions and players from 1900 to 1957.
These digital galleries have so much visual reference and research; I highly recommend taking the time to look through it all and bookmarking or taking note of what you might find useful in the future.
Research is a vital skill for a props person. We may be given a vague description of an object or item and be expected to build something that is either historically accurate, or something that looks “correct”. For example, we all know what a dog looks like, but when we sit down to sculpt one, our minds become incredibly blank; details like the shape of the head, the proportion of the features, and how parts transition between each other are what will sell the prop. Even when a director or designer provides us with full drawings or draftings, we may still need to do research of our own to fill in the blanks or flesh out the specifics.