Google updated their format for how you view pictures apparently. I didn't change anything. If you click on a picture the whole post's pictures are displayed as a thumbnail stream at the bottom.
Each picture still has its own link located on the lower left after you bring one up in the new mode. If you click the link, you can get the old way of viewing and after opening a single picture that way, you can click the picture again to make it bigger just like before.
To get out of thumbnail stream view, click the X in the upper left corner.
I kind of like the new picture viewing formatting in some ways and in some ways not. I am not even sure if I can change things back, I haven't read up on it and am not the one to tinker under my blog's hood for fear of screwing things up beyond repair.