why would you block google images? Waste of traffic i would say ..
I know their layout redesign cost us a lost of images traffic, yet it is a workaround here. With simple tweak i managed to pull ~70% of my images traffic back to my website.
I used to get 15k/day from google images. After template change this number plumped to 1-2k.
So, i tweaked my images a bit and now pulling back ~10k/daily