A lot of images are a complete waste of readers time and bandwidth. If you really must post an image, then please make sure it is relevant, and not just something that would be added to a kindergarten book. Posting the link to a photo is often quite sufficient, and it avoids the stupid quoters who have to clog up the thread with multiple copies of the image.
Another thing that is very important when posting images is to resize image to the size customized for the forum, that can help that pages loaded fast. We have clear rules for avatar images, but as far I know there is no rules for size of other images, maybe this is something what should be added to forum rules. A good part of the forum users probably have very low internet speeds, and some threads with with very large images are not easy to open.