Start off by saving your photo so that it is easily available on your computer.
(Make sure it is of decent size, if not make sure that the image-hosting program you use will do that for you)
Go to http://www.imageshack.us
Find your file. Resize your picture.
Select the bottom link, save this somewhere.
Find the thread in which you wish to post this picture in.
Insert the following text:
<img src="Your Link Here">
This will then appear as your picture.
Whilst inviting frantically, if you don't feel like adding personal text each time...
Feel free to use this as your invite text, just copy paste:
<center>This is a cult for anything, and everything. There will be topic debates, advice, competitions, and games as long as they don't clutter the wall. Every decision will be voted on by the cult members, the goal is that the staff does not dictate and just
do as they please. The cult is free for anyone to join and posts are not moderated.
<br><img src="http://img143.imageshack.us/img143/7923/34143195yr4.gif">
</center>
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