Use OCR.NET component to retrieve text from image, for example from scanned paper document.
uses Tesseract OCR engine and Leptonica image processing library
available for .NET 2 - 4.7
source code included in registered version
royalty free distribution in applications

Xamarin Forms is great if you want to develop apps for different mobile platforms. But when it comes to touch gestures, it is still very limited.
For more than a year they only had the TapGestureRecognizer. Although they did add some others lately, they still don't provide all information which you need. Furthermore the API which they use has been copied from iOS and is not what a .NET developer would expect.

Telerik UI for Xamarin uses the Xamarin.Forms technology, which makes it possible for developers to build native iOS, Android and Windows Phone apps from a single shared C# code base. The Telerik Chart and Calendar for Xamarin enables developers to easily implement various charting functionalities in their Xamarin.Forms projects and achieve the same scenarios across platforms using a single shared C# code base.

LiveXAML runs while you are debugging your application inside an emulator. Whenever you save any XAML file, it automatically updates the running application. LiveXAML has no restrictions on libraries or code usage. You can interact with the interface as you normally do. No additional configuration needed besides initial installation.

Syncfusion, Inc., the developer solutions company of choice, announced its second volume release of the year: Essential Studio 2016 Volume 2, adding enhancements and features across all supported platforms. Two suites in particular Essential Studio for Universal Windows Platform (UWP) and Essential Studio for Xamarin received substantial enhancements.

Xamarin Forms is great for developing apps on Android and iOS but it is missing some important features:

Scalable images
PCL and SharedLibrary, multi-screen / multi-resolution image management
HTML formatted text for labels and buttons
PCL and SharedLibrary custom font management
Android developers can use NinePatch bitmaps, the drawable directory naming convention, Html.FromHtml, and a bunch of complex file manipulations to address the image issue. Likewise, iOS developers can use ResizeableImageWithCapInsets, the @2x, @3x, @4x file naming convention, and some 3rd party libraries for this purpose. Forms 9 Patch enhances Xamarin Forms to make multi-resolution / multi-screen image management, custom fonts, and HTML text formatting easy for PCL and Shared Library apps for iOS and Android.

This Xamarin Forms component that makes it extremely easy to render the native video player on every mobile platform and respond to common video events all from shared Xamarin Forms code. This component provides a highly customizable development experience with a solid foundation to develop rich and visually interesting cross-platform mobile video playback.

Telerik UI for Xamarin uses the Xamarin.Forms technology, which makes it possible for developers to build native iOS, Android and Windows Phone apps from a single shared C# code base. The Telerik Chart and Calendar for Xamarin enables developers to easily implement various charting functionalities in their Xamarin.Forms projects and achieve the same scenarios across platforms using a single shared C# code base.

An essential set of 158 flexible, reliable and high-performance controls and libraries, for all Windows platforms. UI controls for your application front-ends, and data handling libraries for the back-ends. Frequently updated, and backed by a responsive support and development team whose sole ambition is your complete satisfaction.

Xamarin Forms is great for developing apps on Android and iOS but it is missing some important features:

Scalable images
PCL and SharedLibrary, multi-screen / multi-resolution image management
HTML formatted text for labels and buttons
PCL and SharedLibrary custom font management
Android developers can use NinePatch bitmaps, the drawable directory naming convention, Html.FromHtml, and a bunch of complex file manipulations to address the image issue. Likewise, iOS developers can use ResizeableImageWithCapInsets, the @2x, @3x, @4x file naming convention, and some 3rd party libraries for this purpose. Forms 9 Patch enhances Xamarin Forms to make multi-resolution / multi-screen image management, custom fonts, and HTML text formatting easy for PCL and Shared Library apps for iOS and Android.