1: The picture has to be on a "photo sharing" site or other web site. In other words it has to have a web site address. If it's on your computer send it to photohut or one of the many photo hosting sits to get your address. If it's on another web site (myspace, facebook) that will work also.
1a: If your pic is from another web site you can use this shortcut to get the web address: right click on the image and a menu will pop up. From there click on "view image". Your address bar will usually change to just the photo address instead of the page address. Scroll over that address and click Ctrl + Insert. This copies it into your clipboard.
2. Once you have your image address look for this picture in the tags lines above the box you type your message in
Click on that and you will get [img] code.
3. Insert your pictures web address between the code (your text cursor should be blinking where the address needs to go).
3a. If you used the shortcut above (1a) now all you have to do is click on Shift + Insert and the address should pop right into place.
4. There is no 4...you are done.
