tested version with most of the final functionality. Still a few known issues, like dragging to a row that extends to multiple lines

CardCreateImageBox.cs

@@ -0,0 +1,25 @@
+using Godot;
+using System;
+
+public partial class CardCreateImageBox : TextureRect
+{
+	// Called when the node enters the scene tree for the first time.
+	public override void _Ready()
+	{
+	}
+
+	// Called every frame. 'delta' is the elapsed time since the previous frame.
+	public override void _Process(double delta)
+	{
+	}
+	public override void _GuiInput(InputEvent @event)
+    {
+        if (@event is InputEventMouseButton iemb)
+		{
+			if (iemb.Pressed && iemb.ButtonIndex == MouseButton.Left)
+			{
+				GetNode<FileDialog>("%CardImagePicker").Show();
+			}
+		}
+    }
+}