I know when I've had trouble in the past I've been able to reduce the size on my photobucket account and they've posted without a problem.
Not posted any pics here though...so can't speak about this site. I don't think I've had my pic taken for years. Aside from one hideous family photo mother insisted on.
Max size for a .jpg is 488kb. If you click "Manage Attachments" under the text box it will give you a list of file types and their max size. You can upload from the "Manage Attachments" box and your pic will appear as a thumb under your post.
If you want to post an image in your post then you're best resizing it to about 600-700 pixels wide so it doesn't stretch the forum page, then upload it to a site like photobucket or tinypic and take the url they give you with the