Assuming you are using Visual Studio 2005+:

Project > Properties (Found At The Bottom) > Resources > Add Existing Item

Then if, for example, your project is called HelloWorld and the image you added was called shark.jpg use the following code to get the image.

Code:
HelloWorld.Properties.Resources.shark
Notice how there is no file extension to shark.

Intellisense will provide you with all the resources you have added.

Take a look at the In This Section in this link: http://msdn.microsoft.com/en-us/library/9za7fxc7.aspx