Need a book cover for a scholarly book? The Metropolitan Museum of Art now has nearly 400,000 images online in medium-res (72dpi, but around 3000px on the longest side), and…
“that the Museum believes to be in the public domain and free of other known restrictions; these images are now available for scholarly use in any media.”
Above: “A Fury Riding on a Monster”, by Cornelis Saftleven, mid 17th century.

Just to mention this link with a book to read or download >>> https://archive.org/details/poeticalworkswit00hoaguoft as Jonathan Hoag was a friend of HPL and surely inspired the Old Zadok Allen character in the Shadow over Innsmouth. Here you can find a preface and introduction of HPL to the poems of Hoag
Another link in Internet Archive is about Writings in the United Amateur, 1915-1922 by HPL Andrew Francis Lockhart, Rheinhart Kleiner, Frank Belknap Long >>> https://archive.org/details/writingsintheuni30637gut
And last but not least, always in Internet Archive, a rich collection of Amazing Stories pub, some with HPL writing inside >>> https://archive.org/search.php?query=amazing%20stories%20AND%20mediatype%3Atexts
All books can be read on-line or downloaded for free
I will finish wit one of my (old) article (in French sorry) about the re-discovery in the US of HPL in the 70’s by an American student in Paris (Paul R. Michaud who will build with his brother Marc the Necronomicon Press)
>>> http://innsmouthmania.blogspot.fr/2013/07/a-paris-lovecraft-vit.html
Enjoy!
It seems the Met is actually being a little whiffly with its rights claim. In the USA it’s apparently well established in law that… “faithful reproductions of works in the public domain do not attract new copyrights”. Therefore, the Met seems on shaky ground regarding its enforcement of ‘scholarly use only’.