I am writing this to hopefully help you and keep you from making the same mistake that I did.
Last week I noticed all of my pictures were gone. I went back to the very beginning of my blog and where all of my pictures had been there was a placeholder with an "!". I had been using a new video tool and thought maybe I was out of memory, space, whatever. I had heard of this before but couldn't understand why I could still create a new post and all my videos were showing up.
I contacted a few friends with blogs running this issue past them and brought it up to a coworker that I like to say is full of "useless knowledge." He helped me make the connection between Google+, Picasa, and Blogger.
This is where you want to listen closely...
I recently signed up for Google+. I noticed that every picture that I had ever posted on my Blogger account had been placed in a Picasa album labeled with my blog name. I thought...."Well I don't want to start my new profile with all of those pictures....so I'll DELETE them and start fresh." This was all from my Google+ account. I didn't make the connection that my Blogger was connected.