Can't believe this is not already posted, but don't see it. There is actually a coffee table book of his art called The Art of the Hobbit: http://www.amazon.com/The-Art-Hobbit-J-R-R-Tolkien/dp/0547928254
Many (all?) of these images could be scans from the book.
The Art of The Hobbit by J.R.R. Tolkien https://www.amazon.com/dp/0547928254/ref=cm_sw_r_cp_api_glt_fabc_VMZKVH3GFGEDXHKF9EAT
If you want to find more of Tolkien's art Hammond and Scull also released The Art of the Hobbit with his illustrations for...the hobbit. And later this year they'll release The Art of the Lord of the Rings!