Joanna, when you have your picture ready, then click on the spot where you want it to go and drag it to that spot. Then click on the picture itself, then click on the tree.
Click on appearance
Alignment
Choose right, left, or center
Then whatever it says at the bottom, submit or insert, I think.
That's it, it will be where you want it, in center or on one side or another with the text wrapped around it.
Don't try to re-size, ATP does that for you. So leave the sizing alone.
Try that in your blog and see if it helps.
