Nope, not at all! I think the forums are coded to automatically resize photos so they fit the post table, but I might be remembering incorrectly. At any rate, you're welcome to do it however you would like.
"I, Sesshomaru, have no one to protect." - Sesshomaru, Swords of an Honorable Ruler "I don't understand a word you say, but I'll defend to the death your right to confuse me."
- Captain Hawkeye Pierce