For those who were on facebook, you can upload an image to use as your avatar, and if that image is too large, you can drag it in the container to set the crop coordinates.
Can someone help me implement this feature in C # ASP.NET
Maybe this will do your job
http://webcropimage.codeplex.com/
To write your own image trimmer, study the source code for this.
This will be mainly the client side. You can take a look at something like Jcrop .
the best resource on this issue is here.
http://blog.mironabramson.com/blog/post/2009/04/Cropping-image-using-jQuery%2c-Jcrop-and-ASPNET.aspx
It does not give exactly what the question asks, but I think Image Resizer is what you should look at.
http://www.imageresizing.net/