upload the image to a free image hosting website: i use TinyPic - Free Image Hosting, Photo Sharing & Video Hosting
step 1:
click the "choose file" button and find the picture you want to upload.
step 2
click the upload button then fill out the 'captcha' box.
step 3
select all of the text in the "IMG Code for Forums & Message Boards" box and copy it.
step 4
come back to the forum, paste the link you copied and it will look something like this
[I MG] http: //i47. tinypic. com /xsvly.png [/I MG]
without all of the spaces