Asp.Net doesn't provide any functionality that would allow you to crop a page on the client side of things. For this, you'll need a client-side solution, such as a jQuery plug in.
I've used this one recently and it worked a treat
If you need to process the image further on the server side, check out Bob Powell's
] wealth of resources on image manipulation in .NET.
The answer to your other question, about saving the image to the database, can be found here
]. There are lots of articles out on the web on this topic if you Bing/Google it.