The first thing you need to do is to move the pictures from your computer to somewhere on the web. You can download a limited number of photos onto this site, or use something like photobucket. when the picture you wish to show is on the web, you use a right click from the mouse on the picture and select properties. The properties dialogue will show location. You select the whole of that data from http: all the way through to the file type identifier (e.g. jpg).
If that file identifier does not end in a graphic file format such as jpg or bmp etc then it will not show.
You copy that location message, then when in the reply to thread box, you need to click on the little icon just above the text box which looks like a couple of mountain peaks on a yellow background. This will open a little dialogue box which has a space for you to click in and then paste the location and select OK. The picture should magically appear.
a warning - if you have selected ann on-line picture store that requires a password to see individual files, this will not work
Some programmes such as photobox provide a click box that allow you to select and copy that location data by a single
Hope that helps.