image source http://touchlab.jp/2011/07/signote-iphone/
image source https://applinote.com/ios/tool/%E3%83%A2%E3%83%8E%E3%82%AF%E3%83%AD/%E5%8A%A0%E5%B7%A5/screenshot?price=free
image source https://liginc.co.jp/web/design/photoshop/153857/3
