HuskyPup - 10:54 am on Jul 22, 2010 (gmt 0)
As for the results pages, it's harder to tell because they are scripting the whole thing and the code is non-obvious, but I don't think they are hotlinking the images there. It looks like they have their own version of the image resized to their specifications, which would be the way to do it to maximize speed.
I had a good look at this last night and it is Google serving up their cached version of the image.
To see what I mean right click in Firefox and you can see "Block images from" and it gives their serving source.
They are showing their cached image from their server but when trying to save the image it is the size as seen on screen and not the actual size as described and it does not show keyword-image.jpg, all are simply images.jpg.
The actual page is shown greyed out in the background however the images are been served from their cache since the image is not always the up-to-date one and when you click the x and shut down Google's image you see the actual page from where the real image is taken. Now the interesting thing is if you go away from that page and then return to it Google's image is then the ACTUAL one from the site.
I know this because the most popular images on my site which were hotlinked are shown without a copyright notice however when doing the above it shows the image with the copyright notice.
Google are probably trying their best to minimise publisher's bandwidth's etc. and it is still only doing this in Firefox for me!