Haven't figured out all the details yet myself. But the secret to posting pictures (and I'm giving away trade secrets here) is:
1) check off the "HTML" box above
2) type in <img src ="http://www.whateverURLyouwant">
Just be sure to get the URL for the picture corect, skip spaces where I did just now, and don't skip spaces where I didn't! And close off the RUL with quotation marks, and the entire command with < > marks.