Even if this sounds hard to believe, Google Image Search started to index images uploaded to Blogger in December 2007. Until this month, all the images were prevented from being indexed by search engines for unknown reasons. This move is closely related to the fact that the images hosted at Picasa Web Albums started to be indexed by Google.
The chart from Google Analytics shows the number of referrals from images.google.com for this blog:
... and here are some results from Google Image Search:
The images uploaded from Blogger's interface are hosted at Picasa Web Albums, but they're also available at subdomains like bpX.blogger.com, where X is a digit. Another Blogger oddity, inherited from Picasa Web, is that you can't directly link to an image (if you click on a link to one of the two images uploaded above, you'll see a dialog that asks you to download the image). Blogger even has a workaround for this silly restriction: it automatically creates web pages that include the pictures (here's a link to the same image, but this time the image is included in a web page).
Images uploaded before August last year, when Blogger launched the latest major upgrade, are still not crawlable.