title: Flutter How to pick an image and convert BASE64 string in web
body: <p>Actually I'm very new in Flutter-Dart.
  And I'm writing an web app. So I should pick images from file path in web. And I should convert the image to base64 code. because I will add the image to my PHP server with my php codes. PHP code is ready. but I don't know a lot of information about pick images and convert base64. Can anybody help me.</p>