Ice forming inside windows

[Ryan Redenius]

I noticed inside my windows that there's a pretty significant amount of ice (see pic below).  Granted, this was taken last week when Chicago was insanely cold, but I also had a tenant complain about the same thing a couple weeks ago and mention that the window was really drafty.

I have tried using weather stripping but it doesn't completely solve the problem.  I would really like to avoid replacing these windows but am looking for solutions to improve the insulation.  Anyone have any advice?  

Thanks in advance!