ImageGear .NET v25.0 - Updated
Mosaic Effect
User Guide > How to Work with... > Image Processing and Cleanup > Advanced Image Processing and Correction > Image Effects > Mosaic Effect

Mosaic Method - Mosaic API provides the following methods:

The mosaic effect divides a bitmap into tiles of a specified size and changes the color of all pixels in each tile to the average color of pixels within the tile.  

Original Image Image with Mosaic Effect

Also refer to the following API for more information: