Pete, uploading up to five attachments per post without using the in-line feature will result in the box at the bottom of the post you mention. Using in-line (the paperclip at the top of the advanced edit box) eliminates the box as there is nothing to put in it as long as you actually do the in-line attachment. The third way folks supply images is by linking to pictures on a server away from SMC. The first two are recommended so that the information stays with the posts in the SCM archive. The latter places the images at risk should the remote server go away or the OP lose the rights to post/store the images on that remote site.
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The most expensive tool is the one you buy "cheaply" and often...