I use
http://www.photobucket.com/ to store my pictures for posting.
Its free and easy to use
Import your pictures to it then chose the pic you wish to post
highlight the IMG and copy and paste it into the 'insert image' on the post page
you can check if its done properly by previewing it before you post.
If the image is too big you can use the edit feature above the picture in photobucket and make it smaller.
HTH
if not too confused - i know what i mean but doesn't mean everyone elsae will