Julie mentioned one source of W.I. photos which she encountered while researching her book, the Mary Evans Picture Library. Mary Evans, an avid collector of old books and photographs, established the library in the 1960s and now, in the digital age, many of the library’s collections are available online, including a great assortment of photos of the W.I.
Because the library licenses images for commercial purposes, all of the images are watermarked to prevent illegal usage. However, you can still have a browse and look at the collection. I’m particularly partial to the photo of the 1950s basket-making class. Plus ça change!