Using Twitter

I have a box of large-format slides that I purchased a couple of years ago on Ebay, and I am trying to identify them.  I know that they are from Moscow and St. Petersburg, and so to give my students a challenge, I am sending out one slide a week for 5-10 points of extra credit, and to make it even more challenging, I'm sending them out via twitter at #nvccEVANSec.
You can also check http://www.ctevans.net/Nvcc/EC/2web.jpg