I'm currently reading The Victorian City by Judith Flanders. In the chapter on prostitution (The Red-Lit Streets to Death) Flanders mentioned a cheap novel about a nice girl's descent into prostitution. This is how I discovered London by Night. I only read bits of it, but the colored plates interested me.
The author, Anonyma, had written many similar books.
This one has lots of illustrations.
I'm pretty sure these are in the public domain, so go ahead and check out these and others here. However, if you purchased the copyright to the illustrations of William Gray, just let me know.