Question: From where can I get image processing libraries in C# .Net?

Answer: 
Have a look at Craig's Utility Library <http://cul.codeplex.com/>

> 
> Image manipulation available:
> 
> 
> * Cropping, resizing, rotating, flipping
> * To black and white or sepia tone
> * Threshold and edge detection (including Sobel and Laplace)
> * Text drawing, watermarks, object drawing helpers
> * Taking a screenshot which spans monitors
> * RGB Histograms
> * Various convolution filters such as sharpen, sobel emboss, etc. along  
> 
>  with the ability to create your own  
> 
>  easily
> * Various other filters such as "jitter", pixelate, sin wave, median  
> 
>  filter, and dilation, -red/green/blue 
>  filters
> * Multiple blurring techniques including box blur, Gaussian blur,  
> 
>  Kuwahara, and Symmetric Nearest  
> 
>  Neighbor blur
> * Bump map and Normal map helpers
> * ASCII art generator
> * Adjust brightness, gamma, and contrast
> 
> 
> 

Also you may like: [OpenCVSharp](http://code.google.com/p/opencvsharp) and [EmguCV](http://www.emgu.com) - by the way, EmguCV the most advanced one.
Beside the framework functions I like [Image\_Processing\_Lab](http://www.codeproject.com/KB/GDI-plus/Image_Processing_Lab.aspx).