In .NET, there is a class called System.Drawing.Image. You use it to manipulate image data. You can create an instance of this class by calling the static System.Drawing.Image.FromFile() method, passing it a filename. Now, if the filename you pass does not exist, this method throws, very sensibly, a 'FileNotFoundException'. So far so good.
Pop quiz time: what exception does this method throw if the file you provide exists, but is not in a supported image format?