1. First, you need to have a place to host your images. Personally, I use
flickr because it's really clean (you can use your yahoo log in if you have one). But there are others such as
photobucket
2. Once you have uploaded your pictures to that site, go to the picture and select sizing options. For example.. When I'm on flickr, I click "All Sizes" then "Medium"
3. Then, right click the image, and select "Copy Image URL"
4. To post your picture in a thread, click the "Insert Image" icon. Looks like this:
5. Right click again and paste the previously copied URL, then click "OK".
Now there is no reason why anyone shouldn't be able to post their own images.