Signature images should be under 100 pixels tall by 350 pixels wide of image size and 100kb of file size. Avatars are limited to 225 (height) by 140 (width) in size. and 100kb of file size. Animated avatars are allowed, but annoying ones will be subject to change. Animated avatars must meet the same criteria as non-animated avatars.
First off, the limits are absolute. That means that an avatar that measures 226 x 140 won't be permitted any more than one that's 300 x 140. That applies to file size as well. If it's over 100 kb, even if it's only by 1 kb, it won't be permitted. The same goes for signature images.
When I catch them -- and I will eventually, count on it -- I send out warnings to remove the image until it can be modified to comply with the rules. That means that you need to go into your forum profile and remove the image the next time you visit the site. If you put it off, then we're just going to edit your profile ourselves. If we do, and you upload the same oversized image again, you can rest assured that you'll be banned.
Lastly... Show some consideration for others in regards to the images. If it references religion, race, creed or sex in any way, it's probably going to be offensive to someone. So don't post that kind of image, no matter how innocent your intention might be. Keep the images neutral.
Non-hentai anime images and personal images, or photographs that do not touch on potentially offensive subjects are preferred. While these points are not spelled out in the rules, that's because they should be common sense. If I run across any more of them, we will edit the rules to ban such images. It's happened twice since I became a staffer, and that's two times too many.