Yeah, for majority of us, this kind of question will end up with LoL, but after running my very own gaming forum (solarose.niceboard.net), this kind of question always pop up from time to time. So, i made this guide (and post it at my forum originally).
Go to http://imageshack.us/
click on browse button…
chose your desire picture, click open
click host it….and wait a while…until the page below appear
scroll down the page untill you see this one…direct link to image
copy the address (URL)
open up forum …and start to post your mesage.
Click on Image button, paste the URL and click on ok button..
your picture will appear shortly.