If you click on the "scenery" button (to the right of the paper clip in the message menu bar above your text) you will see the screen below - you can enter the URL of a picture that is already hosted on the internet, or you can just drag & drop pictures directly from your PC / device onto the big white arrow, or browse your PC / device and select the images. Once they show hit upload top right . JPGs, PNGs or GIFs can be uploaded. Other file types may be possible.
