Yes, you can go back and add images later. I just tried to make sure. Yep.
The only thing that I notice is that...when you are first creating the blog entry you are allowed to "preview" what you have written and also see the images before
publishing the blog. When you go back later and change/edit the text, add updates, add images, etc. the option to "preview" is listed but the whole world will see it as soon as you select preview. No worries; if the images are sideways like what just happened to me
, you can go back and do another edit.