That is not a "border" issue. To do what you want, you need to set text-decoration: none for links around your images. Edit the vault_css_images template in the Wiki Style Manager and add what you need.
There should not be a problem with the image updating on articles where it is actually used. A link to the attachment is cached, but only uses the static thread ID of the Image page. So this information would be correct no matter what change you made to the article. Also note, the image caption is not linked to the image page's description in any way.