Custom widget for responsive images: Implement the code-behind of the ReponsiveImage widget 
The ResponsiveImage class inherits the SimpleView class, which is a widely used Sitefinity CMS class that provides the basis of all script widgets. 
In the ResponsiveImage class:
    - By overriding the LayoutTemplateName property, you specify the template that you are using. 
 
    - By overriding the InitializeControls method, you include the original image URL and ID and set the responsive image URL. 
    You can use this as a base for comparison between the responsive and original images. 
In Visual Studio:
    - In the context menu of the ResponsiveImages project click Add »  Class...
 
    - Name the new class ResponsiveImage.cs
 
    - Implement the code of the ResponsiveImage.cs file.    
 
 EXAMPLE: For more information about the content of the file, see the ResponsiveImage.cs file of the downloaded sample project.