The Romantics and Victorian Collection has over lo-res 1,300 images, many (if not all — I haven’t checked) in the public domain and available on a Creative Commons Public Domain Mark 1.0 licence, so are available for commercial use. You need to right click the image.
There is also a database of fully searchable public domain British Library images with “no known copyright restrictions”, hosted on flickr.com which the BL is keen to encourage you to explore and re-use.
See also Picturing Places, an online resource which will help researchers visualise the Georgian period. “Discover the role and history of topographical views, maps and texts through over 500 examples from the British Library’s collections and beyond, with fresh research in over 100 articles and films from an academic conference hosted by the British Library and Paul Mellon Centre for Studies in British Art.”