According to MSDN Picture Library Slideshow web part is used to display the pictures in a picture library slideshow.
Below are provided some details about how Picture Library Slideshow web part works:
Step 1. Query Picture Library
Step 2. Initialize and render Slideshow control
Information about Picture entries is passed to the client side and Slideshow control is initialized
Extending Picture Library Slideshow web part
Picture Library Slideshow web part class is marked as sealed, so it could not be extended by inheriting from it . But there is another way how it could be extended.
As was noted earlier SlideshowObject is instantiated using object constructor. Using the technique with overriding SlideshowObject constructor it is possible to provide additional logic as shown below:
For example, the following example demonstrates how to exclude pictures with no titles from displaying them in Slideshow :