If you want to include a picture within a post-
(not the persona/profile/avatar image that appears next to the member name on their post each time) you need to have the picture available already uploaded online.
If you have a picture already uploaded online-like on Flickr, Facebook, Picasa, Picapp, Photobucket, a personal website, etc-then you just use the url for that picture.
Be sure you own the picture or have permission to use it
(There are some free use picture sites so if you want a generic shamrock or beach or whatever out there but they will ask you to link back to their site. Please follow any rules the picture hosting site requires)
Once you have located a picture you want to use-find out the URL. For the example, I will use a picture here on WebMD:
For example-we have a picture of a sink on WebMD that has this as the URL:
https://img.webmd.com/dtmcms/live/webmd/consumer_assets/site_images/modules/healthehome/healthehome_promomodule_rr_bathroom.jpg To include that in the post, click the photo icon at the top of this box (It is the one that looks like a blue square in a Polaroid-sort of) I paste that entire url into the pop up box and here is that picture: