As writers and readers, we take copyright seriously. The rule of thumb here in the forum is to allow 200 to 300 words from a novel-length work, 100 to 150 words from a lengthy non-fiction article, long blog, short story or equivalent, and only a short sentence or single line from a shorter work. Short poems and song lyrics are especially difficult. Essentially, they can't be quoted at all, either in a message or in your forum signature. The source of material taken from a copyrighted work should be cited appropriately.
Photographs and drawings are copyrighted material, too. Unless you took the photo or made the drawing yourself, or have permission from the person who did, you can't post it on the Forum.
Material from web pages (including photographs) should generally be referred to by providing a link to the original source, rather than copying the material directly into your message or attaching it as a file. When possible, use embedded links to keep your message readable.
Material from emails may not be posted on the forum, unless you wrote the email yourself or explicit permission to repost is given in the email. Likewise, the contents of private messages may not be posted on the forum unless both the sender and the receiver of the private message have given permission to post it.