When I first started blogging, I used the "compose" option for creating posts. After a couple of weeks fighting to get the pictures to appear where I wanted them, I switched to "HTML". Much better! Until... recently I tried to get bigger pictures. I saw other blogger blogs showing pics much bigger than I could get, no matter how I tried.
NOW I KNOW: to get pictures "x-large" or "original size", you *have* to switch to "compose" mode. In compose, click on the added pic, and you can get it to show larger. This can be done on old pictures, too. And they even show larger than when clicked... for an example, see the pics here - they get *smaller* when clicked)
(Just in case others have been frustrated too)