Some of these sites provide tags for linking to or embedding images in webpages. If yours does not, type <[img src="image url"]> but do not include the [ and ]. To get the url I'd suggest clicking the picture to view it and copying the address from the address bar.
It is recommended that you link to videos and audio files. To get the url, click to watch the video (or listen to the audio) and then copy the contents of the url bar in your browser. Then follow the directions for posting links.