If the attach image is still an option when posting you can use that, but please resize you pictures so that don't fill more then the screen size. Also compress the file for space/size as best you can.
If it's a picture that is hosted by another site.
For example:
http://us.a1.yimg.com/us.yimg.com/a/...0x130_gen2.gif
use [img] in front and [/img] behind the link to get this
