This seems to be a US only feature – that is you must have a US IP address to see it. Google seem to be censoring their results more and more like this based on IP address – there is a similar blocking of Google Print pages from showing up to non US IP addresses.

I've more info, and the way I get round this in my blog post at http://zmarties.blogspot.com/2005/02/google-images-on-main-results-page-for.html

I don't know it appears the recent shakeup/dance has them even indexing images and being influenced by image names....
guess it may be a backlash of the Picaso beta.