Sept 30, 2015 update:
Blogspot now can be served with HTTPS.This method below can be used for Blogger blog with custom domain.
Apparently the images served from googleusercontent.com, especially the ones on Blogger comment section, are still using
Let's combine the earlier post about switching the blogspot.com images' protocols with this one, the googleusercontent.com images.
About the placement and all related whys (why, but more than one), go to this post