How to handle blank picture in C#

I dont know if I can make this clear, but I'll try (mod, if this is in the wrong section, you're welcome to move it).

Let's say I have a picture that is outside of our domain (like http://www.something.com/test.jpg)

Now I would like to have some code that would allow me to detect if this picture is good, or if it's just an invalid url or a blank picture (because if it is, I want to remove it from my page).  Is there any way to do that (in C#)

 Thanks a lot for taking the time to read this. 
...