Problem is when a member deletes his pictures or posts then you loose the information. When you link to threads out side or link to pictures outside of the site you run a very big risk of that site changing the way they link or upgrading their site to another language and then all those links are broken and then the information is lost and the post is of no value to anyone.

And yes that was a problem at OG when they tried it in the early days. That is why they hosted the pictures too and most other major sites do.