Not sure if this is the place for this, but I just can't think of any better place to ask.
During the pandemic, I found great join in looking through the large visual digital collection of the Metropolitan Museum of Art:
https://www.metmuseum.org/art/the-collection
They have a great collection, the images are usually tho not always in public domain, and the short blurb accompanying many specimen are incredibly well written.
I am interested to know if there exist any other museum or collection house also have similar digital database of their collection? The era I especially enjoyed are the 1750 - 1850 period, so perhaps museum who happen to focus on that period (Napoleonic era, US war of independence, Qing China, late Edo japan, etc) would be greatly appreciated, but any museum like so would be awesome too.
The British Museum (https://www.britishmuseum.org/collection), Victoria and Albert Museum (https://www.vam.ac.uk/collections?type=featured) and Imperial War Museum (https://www.iwm.org.uk/collections) are all top tier collections which number in the millions.
You may also be interested in the Tokyo National Museum (https://artsandculture.google.com/partner/tokyo-national-museum?hl=en), the Ashmolean Museum (https://collections.ashmolean.org), the Royal Maritime Museum (https://www.rmg.co.uk/collections) and the National Museum of China (https://en.chnmuseum.cn/collections_577/)
Sorry for the late answer on this, but many museums today have their collections at least partially digitized. I'll add some more from U.S. art, decorative and history institutions that have notable collections from your time period and good online collections:
Decorative Arts/Art:
Winterthur Museum Gardens & Library: [http://museumcollection.winterthur.org/] (Currently down for maintenance)
Museum if Fine Arts, Boston: [https://www.mfa.org/collections]
Peabody Essex Museum: [https://www.pem.org/explore-art]
Philadelphia Museum of Art: [https://www.philamuseum.org/search/collections]
Museum of Early Southern Decorative Arts: [https://mesda.org/collections/mesda-collection/]
History:
Williamsburg: [https://emuseum.history.org/]