A vast collection of images, some in special collections. Of particular interest is the collection of British Cartoons. 9,000 cartoon prints (approximately 8,500 distinct images) published primarily between 1780 to 1830, and including works by James Gillray, George Cruikshank and Thomas Rowlandson. Not all have been digitised but if you request photography you will receive a projected date for availability. Some, but not all, are downloadable as hi-res .tiff files suitable for reproduction in print. Check copyright for individual images. Many of them have no copyright restrictions.
There is also a collection of about 27,000 LoC public domain images on flickr.com.