Plan59.com is a for-profit website / online museum dedicated to the commercial art of mid 20th century America. They are a very slick looking operation and they offer users an assortment of gifs, jpegs, and even tifs. The "audience" for this website includes advertising companies, publishing companies, the nostalgic public, educators, and non-profit organizations. They also sell prints of the images contained on their site. Therein lies the chief selection principle behind this collection: is it quirky, nostalgic, and would anyone want to purchase the rights to use it?
The images themselves are cleanly scanned and organized into different galleries by topic. Unfortunately, the for-profit nature of this site rears its head when one tries to enlage an image--clicking on the image moves the user on to the next image. The hi-res section of the website contains an invitation to make an offer for use of one of the images presented elsewhere on the site. This site has a nice collection, but it isn't giving much away. That said, the design of the site is very attractive and professional looking. It would have been more attractive if it had included a search feature.
Under the "More" section of the home page, I discovered the closest thing this site has to a curated gallery. There are favorites-ish galleries selected by the staff. Yes, its true that they aren't really well put together in a way that resembles a good digital library. But, they do have a gallery called Demonic Tots and Deeply Disturbing Cuisine.
Metadata on each item in the collection is limited. In some instances, there is infomation on the date and publication from which an advertisement was culled. Other times, there name of the artist may be included. Most of the time, the visitor is forced to let the images speak for themselves. As no images were given substantial metadata properties, quickly moving through them is not possible. At least the images are fun to look at.