It's a fact that people have been taking pictures of lovely ladies for as long as there have been cameras. There's something about really old photos that has always seemed particularly luminous and compelling to me, some combination of the film and retouching techniques that is reminiscent of an oil painter's brush strokes. (And, if you look closely, you can even occasionally see where some tiny brushwork was applied for some proto-Photoshopping.)
The public domain (in the United States) includes images from before the year 1924, which encompasses the Victorian and Edwardian eras, the Belle Epoque, WWI, and the beginning of the jazz age. Some of the photos have a timeless appeal (I often find the eyes particularly compelling in these old portraits), and some are amusingly dated. These older pinups bridge the languidity and restfulness of the classical painted figure and the ever-so-charming (but somewhat contrived) poses of those cheerful mid-century pinups.
The images I've shown today have been sourced primarily from Wikimedia Commons or DeviantArt's Resources & Stock Images category, where several users have uploaded brilliant galleries of these old photos. All photos found on DeviantArt link back to the uploader, and I highly recommend you peruse their galleries for additional works. I tried to find more information about these photos via Google's reverse image search, Wikipedia, and the like, but if anyone is able to provide any confirmed additional information about these photos, such as the year, subject, or photographer, I would love to know and add it to the caption.