Just stumbled upon this old question, in case anyone is still searching I figured i'd update.

Flutter implemented contentInsertConfiguration parameter for TextField and TextFormField in Feburary 2023.

See more here: https://api.flutter.dev/flutter/material/TextField/contentInsertionConfiguration.html

TextField(
  contentInsertionConfiguration: ContentInsertionConfiguration(
    allowedMimeTypes: const <String>['image/png', 'image/gif'],
    onContentInserted: (KeyboardInsertedContent content) {
      final Uint8List? data = content.data;
      if (data != null) {
        // Display in your UI using Image.memory
      }
    },
  ),
);