not resolved yet? I'm also looking for the same problem
I know LINE uses Open Graph tags from websites to generate URL previews. I have same question about where it cached and how to refresh URL previews when people sharing links.
Open Graph tags used by LINE:
# Open Graph tag Example
1 og:image <meta property=”og:image” content=”http://static.naver.jp/line_lp/img/ogp.png”>
2 og:title <meta property=”og:title” content=”LINE : Free Calls & Messages”>
3 og:description <meta property=”og:description” content=”LINE is a new communication app”>