when you click the "reply" option, there's a tool bar. on the tool bar there is a smiley face; on the far left of the box that the smiley is in, there is a little icon of a house, with a sun. you click that and then click "choose files" to upload pictures. if you didn't understand this explanation, you can always just hover your mouse over each icon, until you find the one that says "insert image"