The first website is historypin. This recent entry out of the UK provides a unique way to combine old historical views (worldwide) of street scenes with the more recent Street Views available in Google Maps. The historical images can be switched on and off to allow you to see them superimposed on the way the street looks like today. The site encourages users to upload their own images although in the current beta release version uploads are limited to five per user. There is also a place to annotate the photos under what the site calls Stories. The site has a little over 29,000 photos "pinned" at this point and is definitely worth a look. There is a map view that lets you enter an address to see if there are any photos in locations that interest you. Your best bet at this point is to look at the larger cities.
The second website, similar in concept, is SepiaTown. This site also encourages you to upload your own images and shows the historical image in a side-by-side comparison with the current Google Street View of that location. The website allows viewers to leave comments or share the photos through various social networking sites. SepiaTown is also a relatively new entry and I haven't seen much in the way of posted comments but the photos are interesting and seem distinct from those on historypin.
All of these site are getting at a new way of social networking historical images. If they can get enough users, the power of the network will allow all of us to benefit with the accumulated knowledge that is in our collective heads. I hope they live long and prosper. But I think these sites are just the beginning experiments in how to plumb the depths of our knowledge about the more recent past. The pictures are interesting but they lack so many other ways in which they could be made even better. For example, how about building links to Wikipedia articles or automating a simple Google search of keywords. Which brings up another point: none of these sites allow tagging the images which would help to build out a set of images. Other connections could include the vast libraries of online images in Flickr, Picasa, or any number of other photo sharing websites. Online databases of historical newspaper articles could supplement the images in some cases. Just some thoughts.
If you know of any other websites like these or have any other suggestions on how sites like these could be improved, I would appreciate hearing about them. Drop me a comment!