1. Why am I not allowed to post pictures on threads from the Internet and my PC?
Post the link to an image inside the IMG tag to embed images hosted elsewhere. Use the
button to bring up the IMG tag.
If the image you want to post is on your PC, upload it to an image sharing site like photobucket or imageshack, and then post the link here (inside the IMG tag).
2. If I have replied to a thread how can I stop receiving notifications from the thread when a new reply is given, if I want to?
You mean how can you stop the thread appearing in your unread replies list? I don't think you can.
3. If I don't write in any thread how can I receive notifications about it?
Again, you mean how can you see that thread in your unread replies list? You can't but there is another list called "unread posts" which will show you all unread threads. I check this page a lot.