Thanks for prompt reply and support.
As I mentioned earlier, we need to integrate annotation functionality in SharePoint 2013 custom web part and not using SharePoint Apps.
Here are some issues with Provider hosted App:
1. Our client won't allow us to host the application on third party cloud premises. Even hosting the single piece of functionality would be overhead and not cost effective
2. Consistency: Our current development architecture is based on web part only, going with SharePoint App is not possible at this stage of the project
Kindly provide a sample for the same. Seeking for cooperation and looking forward for sample project.