I'm glad to see that I'm not the only one who has grey images. I'm also using FTM 2012, Windows 7 and merged 2 of my trees that were on FTM and ancestry.com.
Some images did well with the transition. Others are grey, and as noted earlier, if I click on the grey "placeholder," the picture appears. It reverts back to grey when I close it.
I made a minor change to my online tree and have just resynced my merged trees. I have one person's profile up, and I notice that located in the upper right-hand corner is a spinning "wheel" of ancestry leaves - as if something is being processed.
Update - I logged off of ancetry.com, closed FTM, and rebooted my computer, and I no longer have grey "placeholder" photos. I'm not sure if the logoff/reboot helped, but the problem seems to be resolved with my gree.