A few interesting sites but much more found under
PHOTOGRAPH RESTORATION AND DATING-
ResourcesCARTES DE VISITE AND CABINET CARDS (RC topic on Photo Restoration board)
Dead Fred Genealogy Photo ArchiveRoger Vaughan Picture Library:
Date an Old Photograph.
Victorian & Edwardian Photographs and much more
Portrait & Studio Photographers in the UK: 19th & early 20th century- Rosemary and Stan Rodliffe's Index; also includes a section on dating photographs
Photographs from the Lafayette Studio- Society ladies, Indian maharajas, actresses and young men with their new cars were some of the subjects photographed by James Lafayette in the late 19th and early 20th century. This database contains over 600 portraits produced by his studios and was developed over 10 years by Russell Harris, with generous funding from the Elm Trust, who generously donated it to the V&A.
National Archives' photostream- lots of photos: Americas, Caribbean, Asia, Africa, Canada, etc. on Flickr.
Old U.K. PhotosScience & Scoiety Picture LibraryPhotos of the Great WarPictures of the Past- Derbyshire & Nottinghamshire
Victorian Images- artwork and cartoons, CDVs and other photographs, Costumes, etc.
National Portrait Gallery- search by sitter or artist surname within over 185,000 portraits.
Your Paintings (BBC)- "all publicly-owned oil paintings in the UK are now available on this website. 210,000 paintings. Amazing! I've found a few portraits of interest to my research lines - and there's lots more" (thanks to GrahamSimons)
Wigs on the Green- portrait miniatures, silhouettes, portraits & provincial art from the 18th & 19th centuries
Links checked July 2013