These are online sources for images, artwork, advertisements, etc. They are not all specific to food, but include food images that may be used freely for research or illustrations. They do have varying standards for attribution, so please note the permissions or attribution requirements before use.
The Library of Congress has an immense collection of prints and photographs.
The Getty trust has an archive of thousands of searchable paintings, acquisitions, and more.
The Met recently released hundreds of thousands of images, too.
Adflip has a more extensive archive for paying subscribers, but a number of ads in each decade are available for free.
Free Vintage Posters is what it says it is; high concentration of art nouveau.
Modern Mechanix offers scans and transcriptions of ads from the magazine by the same name.
Vintage Ad Browser is helpfully arranged both by subject and by decade, and indicates sources for most of its images.
Penn Libraries has a more extensive list of resources for historical advertisements.
- Photography, Stock and Otherwise
The U.S. Department of Agriculture uploads thousands of photographs that may be used for free with attribution without editing.
Publicdomainpictures.net features photograph that can be used for free, with varying rules for attribution.
Archive.org is a great resource for all kinds of media, but they have a particularly wonderful video archive. I’ve mainly used the Prelinger Archives and Ephemeral Video for pieces to discuss in graduate courses, but that is only scratching the surface.