Why does Image.FromFile keep a file handle open sometimes?

I am doing a lot of image processing in GDI+ in .NET in an ASP.NET application.

I frequently find that Image.FromFile() is keeping a file handle open.

Why is this? What is the best way to open an image without the file handle being retained.

• NB: I'm not doing anything stupid like keeping the Image object lying around - and even if I was I woudlnt expect the file handle to be kept active