Is not just to save them - aka don't let them be deleted (which users can't do anyway) but save the images and attachments in the threads.
There are a lot of usefull threads, like topology research, modeling, shader specific threads etc. Great 5 star rated threads, with hundreds of replyes, lots of comments from pro guys and just tonns of very, very usefull information. HOWEVER, after a while the pics dessapear. I would assume that the main reason that that happends is because the members have to take some of them off to give themselfs room for more attachment/pic posts. Once the pics are gome the thread becoms practically useless, because the whole thing is based around the pics. Like i.e. topology refs, etc. What I suggest, is that highly rated and obviously usefull, threads with big turn out, and tonns of information will be backed up by the mods and image files stored in a separate folder - (mods folder) where they will survive, and the user who posted them will get the space credited back to them, and the pics in the thread will never get deleted. Eventually, if CGTalk will get a Tutorial forum running, those usefull threads will be linked to the tut forum.