The ISS does cross in front of the Moon and the Sun and there are pictures to prove it. The ISS crosses the face of the Sun in less than a second so it's hard to get a picture, but pictures do exist:
http://blogs.discovermagazine.com/badastronomy/2010/12/30/when-natural-and-artificial-moons-align/#.V23oO7grK70
Here's another time-lapse from 2006, with still incomplete ISS:
http://apod.nasa.gov/apod/ap061014.html
Here is a picture of the ISS crossing in front of the Sun, with space shuttle Atlantis approaching to dock with the ISS.
http://www.space.com/8458-wow-shuttle-space-station-photographed-crossing-sun.html
and another, a couple of days later with the shuttle docked
http://astrobob.areavoices.com/2010/05/28/a-billion-artists-at-work/
Here is a video of two satellites passing in front of the Moon
https://www.youtube.com/watch?v=DT1wSm_iK6o#t=23.805079