As a NeoGAF member you are responsible for what you post. In particular this responsibility includes the result of when you put an image in image tags ([img] [/img]). When you use image tags on an image url to display it directly on NeoGAF, you are hotlinking that image, and many domains have hotlinking protection that will detect this and replace the image you intended to display with an alternate image. This can end up being a simple "hotlinking is not permitted, come visit our website" message, but in some cases it can also be extremely offensive or pornographic content designed to punish the hotlinker.
If you hotlink and end up inadvertently posting offensive or pornographic content in this manner, you are breaking the ToS no differently than if you had posted it intentionally, and you will be banned. Even if it's not offensive content, if you post a thread about breaking news and all of the images in your thread end up dying within five minutes or not displaying at all, it's not the most beneficial outcome for everyone involved. With that in mind, it is suggested that you rehost images you intend on hotlinking through a reputable image host. Image hosting companies can be somewhat volatile, but currently popular free solutions are:
abload.de -- non-English, so may take a few moments to understand how to navigate, but very fast, short on restrictions, and has a batch uploader application.
imgur.com -- popular, moderately restrictive, and has web browser extensions available for convenient use.