This morning my blog was ok, a few hours later, the thumbnail photos on my Homepage were fuzzy. Mine being a custom template it had a code that was recently changed.
After researching the issue, I found a fix on the Blogger forums.
The "data:post.thumbnailUrl" format has changed from /s72-c/ to /s72-c-k-no/.
So, if any of you have this problem, you need to go into the html of your template .
1. Backup your template, just in case it might not work.