Textures.cs

public static class Textures {
		public static string AsBase64(Texture2D texture) {
			SetTextureImporterFormat(texture, true);
			var textureCopy = new Texture2D(texture.width, texture.height);
			var colors = texture.GetPixels();
			textureCopy.SetPixels(colors);
			return Convert.ToBase64String(textureCopy.EncodeToPNG());
		}

		private static void SetTextureImporterFormat(Texture2D texture, bool isReadable) {
			if (null == texture) return;

			var assetPath = AssetDatabase.GetAssetPath(texture);
			var tImporter = AssetImporter.GetAtPath(assetPath) as TextureImporter;
			if (tImporter == null) return;
			tImporter.textureType = TextureImporterType.Default;

			tImporter.isReadable = isReadable;

			AssetDatabase.ImportAsset(assetPath);
			AssetDatabase.Refresh();
		}
	}